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 $204.28   8.422%   $221.4845   $221.48   $221.50   $221.50  
  Purchase #2 $244.78   8.811%   $266.3476   $266.35   $266.35   $266.30  
  Purchase #3 $236.87   6.537%   $252.3542   $252.35   $252.35   $252.40  
  Purchase #4 $120.38   12.634%   $135.5888   $135.59   $135.60   $135.60  
  Purchase #5 $207.37   9.302%   $226.6596   $226.66   $226.65   $226.70  
  Purchase #6 $110.52   3.107%   $113.9539   $113.95   $113.95   $114.00  
  Purchase #7 $135.77   9.790%   $149.0619   $149.06   $149.05   $149.10  
  7 purchase totals = $1,259.97       $1,365.4505   $1,365.44   $1,365.45   $1,365.60