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 $218.66   6.141%   $232.0879   $232.09   $232.10   $232.10  
  Purchase #2 $43.79   8.637%   $47.5721   $47.57   $47.55   $47.60  
  Purchase #3 $98.34   3.228%   $101.5144   $101.51   $101.50   $101.50  
  Purchase #4 $80.91   10.165%   $89.1345   $89.13   $89.15   $89.10  
  Purchase #5 $33.85   6.241%   $35.9626   $35.96   $35.95   $36.00  
  Purchase #6 $134.80   11.204%   $149.903   $149.90   $149.90   $149.90  
  Purchase #7 $162.85   4.706%   $170.5137   $170.51   $170.50   $170.50  
  7 purchase totals = $773.20       $826.6882   $826.67   $826.65   $826.70