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 $163.45   12.773%   $184.3275   $184.33   $184.35   $184.30  
  Purchase #2 $17.97   7.338%   $19.2886   $19.29   $19.30   $19.30  
  Purchase #3 $62.85   11.145%   $69.8546   $69.85   $69.85   $69.90  
  Purchase #4 $84.26   11.124%   $93.6331   $93.63   $93.65   $93.60  
  Purchase #5 $207.98   13.790%   $236.6604   $236.66   $236.65   $236.70  
  Purchase #6 $48.70   4.137%   $50.7147   $50.71   $50.70   $50.70  
  Purchase #7 $210.39   12.632%   $236.9665   $236.97   $236.95   $237.00  
  7 purchase totals = $795.60       $891.4454   $891.44   $891.45   $891.50