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 $54.47   12.175%   $61.1017   $61.10   $61.10   $61.10  
  Purchase #2 $249.74   3.449%   $258.3535   $258.35   $258.35   $258.40  
  Purchase #3 $230.97   9.785%   $253.5704   $253.57   $253.55   $253.60  
  Purchase #4 $62.46   9.808%   $68.5861   $68.59   $68.60   $68.60  
  Purchase #5 $161.25   8.730%   $175.3271   $175.33   $175.35   $175.30  
  Purchase #6 $115.80   13.406%   $131.3241   $131.32   $131.30   $131.30  
  Purchase #7 $17.95   12.678%   $20.2257   $20.23   $20.25   $20.20  
  7 purchase totals = $892.64       $968.4886   $968.49   $968.50   $968.50