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 $10.46   10.770%   $11.5865   $11.59   $11.60   $11.60  
  Purchase #2 $140.96   8.742%   $153.2827   $153.28   $153.30   $153.30  
  Purchase #3 $131.30   5.550%   $138.5872   $138.59   $138.60   $138.60  
  Purchase #4 $218.67   10.302%   $241.1974   $241.20   $241.20   $241.20  
  Purchase #5 $232.40   4.800%   $243.5552   $243.56   $243.55   $243.60  
  Purchase #6 $57.38   11.595%   $64.0332   $64.03   $64.05   $64.00  
  Purchase #7 $135.56   11.529%   $151.1887   $151.19   $151.20   $151.20  
  7 purchase totals = $926.73       $1,003.4309   $1,003.44   $1,003.50   $1,003.50