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 $118.54   11.324%   $131.9635   $131.96   $131.95   $132.00  
  Purchase #2 $248.73   10.811%   $275.6202   $275.62   $275.60   $275.60  
  Purchase #3 $25.56   8.251%   $27.669   $27.67   $27.65   $27.70  
  Purchase #4 $187.39   3.462%   $193.8774   $193.88   $193.90   $193.90  
  Purchase #5 $235.45   13.873%   $268.114   $268.11   $268.10   $268.10  
  Purchase #6 $193.78   3.114%   $199.8143   $199.81   $199.80   $199.80  
  Purchase #7 $250.58   7.850%   $270.2505   $270.25   $270.25   $270.30  
  7 purchase totals = $1,260.03       $1,367.3089   $1,367.30   $1,367.25   $1,367.40