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 $87.90   9.220%   $96.0044   $96.00   $96.00   $96.00  
  Purchase #2 $187.69   11.336%   $208.9665   $208.97   $208.95   $209.00  
  Purchase #3 $49.26   4.129%   $51.2939   $51.29   $51.30   $51.30  
  Purchase #4 $206.73   8.244%   $223.7728   $223.77   $223.75   $223.80  
  Purchase #5 $128.88   10.519%   $142.4369   $142.44   $142.45   $142.40  
  Purchase #6 $74.89   13.465%   $84.9739   $84.97   $84.95   $85.00  
  Purchase #7 $124.81   7.805%   $134.5514   $134.55   $134.55   $134.60  
  7 purchase totals = $860.16       $941.9998   $941.99   $941.95   $942.10