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 $152.48   6.270%   $162.0405   $162.04   $162.05   $162.00  
  Purchase #2 $81.41   13.763%   $92.6145   $92.61   $92.60   $92.60  
  Purchase #3 $15.79   10.402%   $17.4325   $17.43   $17.45   $17.40  
  Purchase #4 $47.96   11.733%   $53.5871   $53.59   $53.60   $53.60  
  Purchase #5 $180.51   12.749%   $203.5232   $203.52   $203.50   $203.50  
  Purchase #6 $61.35   12.697%   $69.1396   $69.14   $69.15   $69.10  
  Purchase #7 $218.41   6.453%   $232.504   $232.50   $232.50   $232.50  
  7 purchase totals = $757.91       $830.8414   $830.83   $830.85   $830.70