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 $229.65   7.199%   $246.1825   $246.18   $246.20   $246.20  
  Purchase #2 $193.98   3.334%   $200.4473   $200.45   $200.45   $200.40  
  Purchase #3 $127.98   3.232%   $132.1163   $132.12   $132.10   $132.10  
  Purchase #4 $69.88   4.608%   $73.1001   $73.10   $73.10   $73.10  
  Purchase #5 $13.42   11.148%   $14.9161   $14.92   $14.90   $14.90  
  Purchase #6 $70.55   6.778%   $75.3319   $75.33   $75.35   $75.30  
  Purchase #7 $20.87   11.564%   $23.2834   $23.28   $23.30   $23.30  
  7 purchase totals = $726.33       $765.3776   $765.38   $765.40   $765.30