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 $212.93   13.351%   $241.3583   $241.36   $241.35   $241.40  
  Purchase #2 $179.61   12.225%   $201.5673   $201.57   $201.55   $201.60  
  Purchase #3 $215.98   7.495%   $232.1677   $232.17   $232.15   $232.20  
  Purchase #4 $15.32   5.598%   $16.1776   $16.18   $16.20   $16.20  
  Purchase #5 $205.83   13.713%   $234.0555   $234.06   $234.05   $234.10  
  Purchase #6 $244.38   5.541%   $257.9211   $257.92   $257.90   $257.90  
  Purchase #7 $85.88   8.865%   $93.4933   $93.49   $93.50   $93.50  
  7 purchase totals = $1,159.93       $1,276.7408   $1,276.75   $1,276.70   $1,276.90