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 $191.97   11.121%   $213.319   $213.32   $213.30   $213.30  
  Purchase #2 $60.71   5.717%   $64.1808   $64.18   $64.20   $64.20  
  Purchase #3 $172.53   7.591%   $185.6268   $185.63   $185.65   $185.60  
  Purchase #4 $125.93   3.751%   $130.6536   $130.65   $130.65   $130.70  
  Purchase #5 $20.57   9.756%   $22.5768   $22.58   $22.60   $22.60  
  Purchase #6 $94.35   13.211%   $106.8146   $106.81   $106.80   $106.80  
  Purchase #7 $35.61   11.674%   $39.7671   $39.77   $39.75   $39.80  
  7 purchase totals = $701.67       $762.9387   $762.94   $762.95   $763.00