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 $221.76   11.641%   $247.5751   $247.58   $247.60   $247.60  
  Purchase #2 $33.47   8.154%   $36.1991   $36.20   $36.20   $36.20  
  Purchase #3 $169.84   5.242%   $178.743   $178.74   $178.75   $178.70  
  Purchase #4 $211.83   7.226%   $227.1368   $227.14   $227.15   $227.10  
  Purchase #5 $178.94   3.158%   $184.5909   $184.59   $184.60   $184.60  
  Purchase #6 $12.85   12.625%   $14.4723   $14.47   $14.45   $14.50  
  Purchase #7 $112.72   5.675%   $119.1169   $119.12   $119.10   $119.10  
  7 purchase totals = $941.41       $1,007.8341   $1,007.84   $1,007.85   $1,007.80