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 $87.77   8.402%   $95.1444   $95.14   $95.15   $95.10  
  Purchase #2 $54.46   5.114%   $57.2451   $57.25   $57.25   $57.20  
  Purchase #3 $181.88   12.515%   $204.6423   $204.64   $204.65   $204.60  
  Purchase #4 $105.34   11.798%   $117.768   $117.77   $117.75   $117.80  
  Purchase #5 $126.90   6.760%   $135.4784   $135.48   $135.50   $135.50  
  Purchase #6 $129.65   5.376%   $136.62   $136.62   $136.60   $136.60  
  Purchase #7 $202.35   12.667%   $227.9817   $227.98   $228.00   $228.00  
  7 purchase totals = $888.35       $974.8799   $974.88   $974.90   $974.80