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 $152.27   11.479%   $169.7491   $169.75   $169.75   $169.70  
  Purchase #2 $169.81   10.826%   $188.1936   $188.19   $188.20   $188.20  
  Purchase #3 $209.73   8.199%   $226.9258   $226.93   $226.95   $226.90  
  Purchase #4 $52.35   5.826%   $55.3999   $55.40   $55.40   $55.40  
  Purchase #5 $62.89   12.386%   $70.6796   $70.68   $70.70   $70.70  
  Purchase #6 $250.36   3.585%   $259.3354   $259.34   $259.35   $259.30  
  Purchase #7 $46.60   12.835%   $52.5811   $52.58   $52.60   $52.60  
  7 purchase totals = $944.01       $1,022.8645   $1,022.87   $1,022.95   $1,022.80