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 $162.92   12.816%   $183.7998   $183.80   $183.80   $183.80  
  Purchase #2 $43.94   4.597%   $45.9599   $45.96   $45.95   $46.00  
  Purchase #3 $87.68   11.222%   $97.5194   $97.52   $97.50   $97.50  
  Purchase #4 $245.43   11.675%   $274.084   $274.08   $274.10   $274.10  
  Purchase #5 $167.48   9.776%   $183.8528   $183.85   $183.85   $183.90  
  Purchase #6 $28.60   6.866%   $30.5637   $30.56   $30.55   $30.60  
  Purchase #7 $119.63   4.684%   $125.2335   $125.23   $125.25   $125.20  
  7 purchase totals = $855.68       $941.0131   $941.00   $941.00   $941.10