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 $60.47   11.648%   $67.5135   $67.51   $67.50   $67.50  
  Purchase #2 $197.62   6.227%   $209.9258   $209.93   $209.95   $209.90  
  Purchase #3 $199.43   8.562%   $216.5052   $216.51   $216.50   $216.50  
  Purchase #4 $64.51   6.616%   $68.778   $68.78   $68.80   $68.80  
  Purchase #5 $142.39   9.141%   $155.4059   $155.41   $155.40   $155.40  
  Purchase #6 $214.67   10.479%   $237.1653   $237.17   $237.15   $237.20  
  Purchase #7 $142.40   8.217%   $154.101   $154.10   $154.10   $154.10  
  7 purchase totals = $1,021.49       $1,109.3947   $1,109.41   $1,109.40   $1,109.40