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 $119.32   12.217%   $133.8973   $133.90   $133.90   $133.90  
  Purchase #2 $50.79   4.341%   $52.9948   $52.99   $53.00   $53.00  
  Purchase #3 $114.96   9.246%   $125.5892   $125.59   $125.60   $125.60  
  Purchase #4 $152.51   4.215%   $158.9383   $158.94   $158.95   $158.90  
  Purchase #5 $204.59   10.577%   $226.2295   $226.23   $226.25   $226.20  
  Purchase #6 $176.85   12.788%   $199.4656   $199.47   $199.45   $199.50  
  Purchase #7 $43.34   9.646%   $47.5206   $47.52   $47.50   $47.50  
  7 purchase totals = $862.36       $944.6353   $944.64   $944.65   $944.60