Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $226.86   7.411%   $243.6726   $243.67   $243.65   $243.70  
  Purchase #2 $236.93   5.684%   $250.3971   $250.40   $250.40   $250.40  
  Purchase #3 $134.87   8.640%   $146.5228   $146.52   $146.50   $146.50  
  Purchase #4 $210.37   5.745%   $222.4558   $222.46   $222.45   $222.50  
  Purchase #5 $112.37   10.753%   $124.4531   $124.45   $124.45   $124.50  
  Purchase #6 $137.32   5.327%   $144.635   $144.64   $144.65   $144.60  
  Purchase #7 $116.54   8.160%   $126.0497   $126.05   $126.05   $126.00  
  7 purchase totals = $1,175.26       $1,258.1861   $1,258.19   $1,258.15   $1,258.20