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 $139.90   9.545%   $153.2535   $153.25   $153.25   $153.30  
  Purchase #2 $158.96   6.439%   $169.1954   $169.20   $169.20   $169.20  
  Purchase #3 $235.85   8.462%   $255.8076   $255.81   $255.80   $255.80  
  Purchase #4 $215.51   9.104%   $235.13   $235.13   $235.15   $235.10  
  Purchase #5 $168.78   4.371%   $176.1574   $176.16   $176.15   $176.20  
  Purchase #6 $231.71   9.626%   $254.0144   $254.01   $254.00   $254.00  
  Purchase #7 $112.52   12.284%   $126.342   $126.34   $126.35   $126.30  
  7 purchase totals = $1,263.23       $1,369.9003   $1,369.90   $1,369.90   $1,369.90