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 $83.41   13.586%   $94.7421   $94.74   $94.75   $94.70  
  Purchase #2 $58.85   5.274%   $61.9537   $61.95   $61.95   $62.00  
  Purchase #3 $90.96   13.419%   $103.1659   $103.17   $103.15   $103.20  
  Purchase #4 $9.53   6.462%   $10.1458   $10.15   $10.15   $10.10  
  Purchase #5 $114.75   4.494%   $119.9069   $119.91   $119.90   $119.90  
  Purchase #6 $125.35   9.731%   $137.5478   $137.55   $137.55   $137.50  
  Purchase #7 $249.50   13.817%   $283.9734   $283.97   $283.95   $284.00  
  7 purchase totals = $732.35       $811.4356   $811.44   $811.40   $811.40