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 $238.64   6.859%   $255.0083   $255.01   $255.00   $255.00  
  Purchase #2 $218.54   13.748%   $248.5849   $248.58   $248.60   $248.60  
  Purchase #3 $159.46   11.655%   $178.0451   $178.05   $178.05   $178.00  
  Purchase #4 $163.63   12.337%   $183.817   $183.82   $183.80   $183.80  
  Purchase #5 $58.86   10.392%   $64.9767   $64.98   $65.00   $65.00  
  Purchase #6 $76.41   12.690%   $86.1064   $86.11   $86.10   $86.10  
  Purchase #7 $101.58   6.503%   $108.1857   $108.19   $108.20   $108.20  
  7 purchase totals = $1,017.12       $1,124.7241   $1,124.74   $1,124.75   $1,124.70