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 $191.53   6.248%   $203.4968   $203.50   $203.50   $203.50  
  Purchase #2 $42.90   6.370%   $45.6327   $45.63   $45.65   $45.60  
  Purchase #3 $80.88   4.608%   $84.607   $84.61   $84.60   $84.60  
  Purchase #4 $7.38   6.107%   $7.8307   $7.83   $7.85   $7.80  
  Purchase #5 $99.90   6.785%   $106.6782   $106.68   $106.70   $106.70  
  Purchase #6 $190.68   9.207%   $208.2359   $208.24   $208.25   $208.20  
  Purchase #7 $172.66   7.331%   $185.3177   $185.32   $185.30   $185.30  
  7 purchase totals = $785.93       $841.7990   $841.81   $841.85   $841.70