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 $70.87   5.372%   $74.6771   $74.68   $74.70   $74.70  
  Purchase #2 $173.33   12.575%   $195.1262   $195.13   $195.15   $195.10  
  Purchase #3 $129.81   5.569%   $137.0391   $137.04   $137.05   $137.00  
  Purchase #4 $210.57   5.680%   $222.5304   $222.53   $222.55   $222.50  
  Purchase #5 $195.67   8.282%   $211.8754   $211.88   $211.90   $211.90  
  Purchase #6 $23.27   10.743%   $25.7699   $25.77   $25.75   $25.80  
  Purchase #7 $122.62   10.381%   $135.3492   $135.35   $135.35   $135.30  
  7 purchase totals = $926.14       $1,002.3673   $1,002.38   $1,002.45   $1,002.30