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 $96.97   8.192%   $104.9138   $104.91   $104.90   $104.90  
  Purchase #2 $185.99   4.317%   $194.0192   $194.02   $194.00   $194.00  
  Purchase #3 $243.97   8.842%   $265.5418   $265.54   $265.55   $265.50  
  Purchase #4 $47.29   3.524%   $48.9565   $48.96   $48.95   $49.00  
  Purchase #5 $29.47   11.428%   $32.8378   $32.84   $32.85   $32.80  
  Purchase #6 $60.69   11.422%   $67.622   $67.62   $67.60   $67.60  
  Purchase #7 $221.65   4.121%   $230.7842   $230.78   $230.80   $230.80  
  7 purchase totals = $886.03       $944.6753   $944.67   $944.65   $944.60