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 $154.36   13.274%   $174.8497   $174.85   $174.85   $174.80  
  Purchase #2 $60.41   10.321%   $66.6449   $66.64   $66.65   $66.60  
  Purchase #3 $82.32   6.860%   $87.9672   $87.97   $87.95   $88.00  
  Purchase #4 $135.67   4.816%   $142.2039   $142.20   $142.20   $142.20  
  Purchase #5 $18.97   10.768%   $21.0127   $21.01   $21.00   $21.00  
  Purchase #6 $167.40   9.178%   $182.764   $182.76   $182.75   $182.80  
  Purchase #7 $81.88   5.467%   $86.3564   $86.36   $86.35   $86.40  
  7 purchase totals = $701.01       $761.7988   $761.79   $761.75   $761.80