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 $48.49   8.762%   $52.7387   $52.74   $52.75   $52.70  
  Purchase #2 $197.77   10.410%   $218.3579   $218.36   $218.35   $218.40  
  Purchase #3 $155.63   3.182%   $160.5821   $160.58   $160.60   $160.60  
  Purchase #4 $124.94   3.391%   $129.1767   $129.18   $129.20   $129.20  
  Purchase #5 $32.92   12.314%   $36.9738   $36.97   $36.95   $37.00  
  Purchase #6 $234.81   6.333%   $249.6805   $249.68   $249.70   $249.70  
  Purchase #7 $149.79   4.767%   $156.9305   $156.93   $156.95   $156.90  
  7 purchase totals = $944.35       $1,004.4402   $1,004.44   $1,004.50   $1,004.50