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 $89.27   4.218%   $93.0354   $93.04   $93.05   $93.00  
  Purchase #2 $170.61   3.306%   $176.2504   $176.25   $176.25   $176.30  
  Purchase #3 $30.41   7.465%   $32.6801   $32.68   $32.70   $32.70  
  Purchase #4 $160.90   3.537%   $166.591   $166.59   $166.60   $166.60  
  Purchase #5 $46.27   3.763%   $48.0111   $48.01   $48.00   $48.00  
  Purchase #6 $125.70   13.865%   $143.1283   $143.13   $143.15   $143.10  
  Purchase #7 $109.92   5.432%   $115.8909   $115.89   $115.90   $115.90  
  7 purchase totals = $733.08       $775.5872   $775.59   $775.65   $775.60