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 $183.97   10.726%   $203.7026   $203.70   $203.70   $203.70  
  Purchase #2 $96.37   10.873%   $106.8483   $106.85   $106.85   $106.80  
  Purchase #3 $14.44   4.606%   $15.1051   $15.11   $15.10   $15.10  
  Purchase #4 $145.76   9.453%   $159.5387   $159.54   $159.55   $159.50  
  Purchase #5 $201.25   12.494%   $226.3942   $226.39   $226.40   $226.40  
  Purchase #6 $56.83   4.758%   $59.534   $59.53   $59.55   $59.50  
  Purchase #7 $20.34   7.779%   $21.9222   $21.92   $21.90   $21.90  
  7 purchase totals = $718.96       $793.0451   $793.04   $793.05   $792.90