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 $229.38   10.744%   $254.0246   $254.02   $254.00   $254.00  
  Purchase #2 $35.42   10.140%   $39.0116   $39.01   $39.00   $39.00  
  Purchase #3 $168.97   5.571%   $178.3833   $178.38   $178.40   $178.40  
  Purchase #4 $49.37   4.820%   $51.7496   $51.75   $51.75   $51.70  
  Purchase #5 $238.28   6.680%   $254.1971   $254.20   $254.20   $254.20  
  Purchase #6 $215.59   3.667%   $223.4957   $223.50   $223.50   $223.50  
  Purchase #7 $147.37   7.393%   $158.2651   $158.27   $158.25   $158.30  
  7 purchase totals = $1,084.38       $1,159.1270   $1,159.13   $1,159.10   $1,159.10