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 $91.38   8.419%   $99.0733   $99.07   $99.05   $99.10  
  Purchase #2 $195.96   3.252%   $202.3326   $202.33   $202.35   $202.30  
  Purchase #3 $46.32   9.160%   $50.5629   $50.56   $50.55   $50.60  
  Purchase #4 $178.66   13.419%   $202.6344   $202.63   $202.65   $202.60  
  Purchase #5 $76.57   12.159%   $85.8801   $85.88   $85.90   $85.90  
  Purchase #6 $210.58   7.789%   $226.9821   $226.98   $227.00   $227.00  
  Purchase #7 $138.76   12.543%   $156.1647   $156.16   $156.15   $156.20  
  7 purchase totals = $938.23       $1,023.6301   $1,023.61   $1,023.65   $1,023.70