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 $29.42   11.127%   $32.6936   $32.69   $32.70   $32.70  
  Purchase #2 $63.44   12.437%   $71.33   $71.33   $71.35   $71.30  
  Purchase #3 $250.91   11.390%   $279.4886   $279.49   $279.50   $279.50  
  Purchase #4 $58.65   9.727%   $64.3549   $64.35   $64.35   $64.40  
  Purchase #5 $90.35   4.495%   $94.4112   $94.41   $94.40   $94.40  
  Purchase #6 $183.70   4.172%   $191.364   $191.36   $191.35   $191.40  
  Purchase #7 $184.87   11.845%   $206.7679   $206.77   $206.75   $206.80  
  7 purchase totals = $861.34       $940.4102   $940.40   $940.40   $940.50