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 $60.68   10.367%   $66.9707   $66.97   $66.95   $67.00  
  Purchase #2 $218.48   13.327%   $247.5968   $247.60   $247.60   $247.60  
  Purchase #3 $157.37   12.566%   $177.1451   $177.15   $177.15   $177.10  
  Purchase #4 $114.80   10.542%   $126.9022   $126.90   $126.90   $126.90  
  Purchase #5 $24.27   12.591%   $27.3258   $27.33   $27.35   $27.30  
  Purchase #6 $100.87   5.369%   $106.2857   $106.29   $106.30   $106.30  
  Purchase #7 $48.39   6.480%   $51.5257   $51.53   $51.55   $51.50  
  7 purchase totals = $724.86       $803.7520   $803.77   $803.80   $803.70