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 $204.82   11.422%   $228.2145   $228.21   $228.20   $228.20  
  Purchase #2 $71.86   4.681%   $75.2238   $75.22   $75.20   $75.20  
  Purchase #3 $173.72   4.827%   $182.1055   $182.11   $182.10   $182.10  
  Purchase #4 $72.75   3.536%   $75.3224   $75.32   $75.30   $75.30  
  Purchase #5 $205.66   6.733%   $219.5071   $219.51   $219.50   $219.50  
  Purchase #6 $73.97   8.715%   $80.4165   $80.42   $80.40   $80.40  
  Purchase #7 $147.57   7.210%   $158.2098   $158.21   $158.20   $158.20  
  7 purchase totals = $950.35       $1,018.9996   $1,019.00   $1,018.90   $1,018.90