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 $235.54   10.206%   $259.5792   $259.58   $259.60   $259.60  
  Purchase #2 $205.45   9.341%   $224.6411   $224.64   $224.65   $224.60  
  Purchase #3 $153.63   9.546%   $168.2955   $168.30   $168.30   $168.30  
  Purchase #4 $95.66   9.322%   $104.5774   $104.58   $104.60   $104.60  
  Purchase #5 $64.82   6.570%   $69.0787   $69.08   $69.10   $69.10  
  Purchase #6 $161.39   13.339%   $182.9178   $182.92   $182.90   $182.90  
  Purchase #7 $113.74   4.824%   $119.2268   $119.23   $119.25   $119.20  
  7 purchase totals = $1,030.23       $1,128.3165   $1,128.33   $1,128.40   $1,128.30