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 $209.97   11.671%   $234.4756   $234.48   $234.50   $234.50  
  Purchase #2 $97.39   6.812%   $104.0242   $104.02   $104.00   $104.00  
  Purchase #3 $81.53   12.556%   $91.7669   $91.77   $91.75   $91.80  
  Purchase #4 $237.96   6.593%   $253.6487   $253.65   $253.65   $253.60  
  Purchase #5 $158.69   9.557%   $173.856   $173.86   $173.85   $173.90  
  Purchase #6 $143.84   11.211%   $159.9659   $159.97   $159.95   $160.00  
  Purchase #7 $6.82   9.842%   $7.4912   $7.49   $7.50   $7.50  
  7 purchase totals = $936.20       $1,025.2285   $1,025.24   $1,025.20   $1,025.30