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 $76.27   7.556%   $82.033   $82.03   $82.05   $82.00  
  Purchase #2 $74.64   13.205%   $84.4962   $84.50   $84.50   $84.50  
  Purchase #3 $33.68   9.362%   $36.8331   $36.83   $36.85   $36.80  
  Purchase #4 $104.54   13.692%   $118.8536   $118.85   $118.85   $118.90  
  Purchase #5 $226.83   6.186%   $240.8617   $240.86   $240.85   $240.90  
  Purchase #6 $187.88   7.548%   $202.0612   $202.06   $202.05   $202.10  
  Purchase #7 $77.47   13.457%   $87.8951   $87.90   $87.90   $87.90  
  7 purchase totals = $781.31       $853.0339   $853.03   $853.05   $853.10