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 $64.75   10.467%   $71.5274   $71.53   $71.55   $71.50  
  Purchase #2 $186.87   9.453%   $204.5348   $204.53   $204.55   $204.50  
  Purchase #3 $231.58   13.199%   $262.1462   $262.15   $262.15   $262.10  
  Purchase #4 $102.47   11.488%   $114.2418   $114.24   $114.25   $114.20  
  Purchase #5 $138.46   9.752%   $151.9626   $151.96   $151.95   $152.00  
  Purchase #6 $204.35   12.229%   $229.34   $229.34   $229.35   $229.30  
  Purchase #7 $210.51   4.870%   $220.7618   $220.76   $220.75   $220.80  
  7 purchase totals = $1,138.99       $1,254.5146   $1,254.51   $1,254.55   $1,254.40