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 $236.51   11.659%   $264.0847   $264.08   $264.10   $264.10  
  Purchase #2 $58.51   8.436%   $63.4459   $63.45   $63.45   $63.40  
  Purchase #3 $131.85   4.575%   $137.8821   $137.88   $137.90   $137.90  
  Purchase #4 $210.89   11.142%   $234.3874   $234.39   $234.40   $234.40  
  Purchase #5 $191.29   6.440%   $203.6091   $203.61   $203.60   $203.60  
  Purchase #6 $221.54   10.475%   $244.7463   $244.75   $244.75   $244.70  
  Purchase #7 $73.44   3.709%   $76.1639   $76.16   $76.15   $76.20  
  7 purchase totals = $1,124.03       $1,224.3194   $1,224.32   $1,224.35   $1,224.30