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 $92.81   12.487%   $104.3992   $104.40   $104.40   $104.40  
  Purchase #2 $55.74   12.349%   $62.6233   $62.62   $62.60   $62.60  
  Purchase #3 $43.46   4.649%   $45.4805   $45.48   $45.50   $45.50  
  Purchase #4 $59.88   8.446%   $64.9375   $64.94   $64.95   $64.90  
  Purchase #5 $77.85   11.263%   $86.6182   $86.62   $86.60   $86.60  
  Purchase #6 $92.34   5.296%   $97.2303   $97.23   $97.25   $97.20  
  Purchase #7 $77.73   12.793%   $87.674   $87.67   $87.65   $87.70  
  7 purchase totals = $499.81       $548.9630   $548.96   $548.95   $548.90