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 $67.99   10.381%   $75.048   $75.05   $75.05   $75.00  
  Purchase #2 $79.81   11.696%   $89.1446   $89.14   $89.15   $89.10  
  Purchase #3 $67.94   12.725%   $76.5854   $76.59   $76.60   $76.60  
  Purchase #4 $127.54   6.237%   $135.4947   $135.49   $135.50   $135.50  
  Purchase #5 $210.82   9.172%   $230.1564   $230.16   $230.15   $230.20  
  Purchase #6 $247.90   9.874%   $272.3776   $272.38   $272.40   $272.40  
  Purchase #7 $228.87   6.253%   $243.1812   $243.18   $243.20   $243.20  
  7 purchase totals = $1,030.87       $1,121.9879   $1,121.99   $1,122.05   $1,122.00