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 $194.48   8.636%   $211.2753   $211.28   $211.30   $211.30  
  Purchase #2 $151.73   6.839%   $162.1068   $162.11   $162.10   $162.10  
  Purchase #3 $85.41   11.499%   $95.2313   $95.23   $95.25   $95.20  
  Purchase #4 $235.26   7.727%   $253.4385   $253.44   $253.45   $253.40  
  Purchase #5 $117.85   11.336%   $131.2095   $131.21   $131.20   $131.20  
  Purchase #6 $100.87   12.761%   $113.742   $113.74   $113.75   $113.70  
  Purchase #7 $25.74   10.738%   $28.504   $28.50   $28.50   $28.50  
  7 purchase totals = $911.34       $995.5074   $995.51   $995.55   $995.40