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 $224.90   10.202%   $247.8443   $247.84   $247.85   $247.80  
  Purchase #2 $68.63   12.299%   $77.0708   $77.07   $77.05   $77.10  
  Purchase #3 $242.36   6.399%   $257.8686   $257.87   $257.85   $257.90  
  Purchase #4 $101.41   8.218%   $109.7439   $109.74   $109.75   $109.70  
  Purchase #5 $140.65   10.246%   $155.061   $155.06   $155.05   $155.10  
  Purchase #6 $94.93   7.507%   $102.0564   $102.06   $102.05   $102.10  
  Purchase #7 $69.98   4.184%   $72.908   $72.91   $72.90   $72.90  
  7 purchase totals = $942.86       $1,022.5530   $1,022.55   $1,022.50   $1,022.60