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 $187.93   12.281%   $211.0097   $211.01   $211.00   $211.00  
  Purchase #2 $84.87   10.840%   $94.0699   $94.07   $94.05   $94.10  
  Purchase #3 $76.43   8.647%   $83.0389   $83.04   $83.05   $83.00  
  Purchase #4 $228.60   5.315%   $240.7501   $240.75   $240.75   $240.80  
  Purchase #5 $60.58   6.224%   $64.3505   $64.35   $64.35   $64.40  
  Purchase #6 $168.27   7.161%   $180.3198   $180.32   $180.30   $180.30  
  Purchase #7 $118.55   11.290%   $131.9343   $131.93   $131.95   $131.90  
  7 purchase totals = $925.23       $1,005.4732   $1,005.47   $1,005.45   $1,005.50