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 $217.73   12.373%   $244.6697   $244.67   $244.65   $244.70  
  Purchase #2 $46.52   6.859%   $49.7108   $49.71   $49.70   $49.70  
  Purchase #3 $171.32   12.672%   $193.0297   $193.03   $193.05   $193.00  
  Purchase #4 $236.56   11.652%   $264.124   $264.12   $264.10   $264.10  
  Purchase #5 $95.93   10.113%   $105.6314   $105.63   $105.65   $105.60  
  Purchase #6 $45.65   9.873%   $50.157   $50.16   $50.15   $50.20  
  Purchase #7 $40.78   5.168%   $42.8875   $42.89   $42.90   $42.90  
  7 purchase totals = $854.49       $950.2101   $950.21   $950.20   $950.20