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 $173.53   11.646%   $193.7393   $193.74   $193.75   $193.70  
  Purchase #2 $155.99   10.429%   $172.2582   $172.26   $172.25   $172.30  
  Purchase #3 $88.82   7.203%   $95.2177   $95.22   $95.20   $95.20  
  Purchase #4 $250.72   8.187%   $271.2464   $271.25   $271.25   $271.20  
  Purchase #5 $225.85   4.874%   $236.8579   $236.86   $236.85   $236.90  
  Purchase #6 $81.26   8.546%   $88.2045   $88.20   $88.20   $88.20  
  Purchase #7 $22.32   6.572%   $23.7869   $23.79   $23.80   $23.80  
  7 purchase totals = $998.49       $1,081.3109   $1,081.32   $1,081.30   $1,081.30