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 $161.85   9.502%   $177.229   $177.23   $177.25   $177.20  
  Purchase #2 $80.39   10.147%   $88.5472   $88.55   $88.55   $88.50  
  Purchase #3 $21.53   11.398%   $23.984   $23.98   $24.00   $24.00  
  Purchase #4 $156.99   11.872%   $175.6279   $175.63   $175.65   $175.60  
  Purchase #5 $212.95   13.321%   $241.3171   $241.32   $241.30   $241.30  
  Purchase #6 $177.86   6.817%   $189.9847   $189.98   $190.00   $190.00  
  Purchase #7 $25.92   7.318%   $27.8168   $27.82   $27.80   $27.80  
  7 purchase totals = $837.49       $924.5067   $924.51   $924.55   $924.40