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 $250.52   12.636%   $282.1757   $282.18   $282.20   $282.20  
  Purchase #2 $208.44   7.259%   $223.5707   $223.57   $223.55   $223.60  
  Purchase #3 $248.89   3.804%   $258.3578   $258.36   $258.35   $258.40  
  Purchase #4 $87.63   8.146%   $94.7683   $94.77   $94.75   $94.80  
  Purchase #5 $213.42   5.750%   $225.6917   $225.69   $225.70   $225.70  
  Purchase #6 $152.53   9.824%   $167.5145   $167.51   $167.50   $167.50  
  Purchase #7 $186.73   13.837%   $212.5678   $212.57   $212.55   $212.60  
  7 purchase totals = $1,348.16       $1,464.6465   $1,464.65   $1,464.60   $1,464.80