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 $56.41   12.561%   $63.4957   $63.50   $63.50   $63.50  
  Purchase #2 $247.89   6.615%   $264.2879   $264.29   $264.30   $264.30  
  Purchase #3 $204.67   10.715%   $226.6004   $226.60   $226.60   $226.60  
  Purchase #4 $125.50   5.441%   $132.3285   $132.33   $132.35   $132.30  
  Purchase #5 $113.54   7.291%   $121.8182   $121.82   $121.80   $121.80  
  Purchase #6 $229.29   11.213%   $255.0003   $255.00   $255.00   $255.00  
  Purchase #7 $29.46   7.836%   $31.7685   $31.77   $31.75   $31.80  
  7 purchase totals = $1,006.76       $1,095.2995   $1,095.31   $1,095.30   $1,095.30