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 $46.68   12.298%   $52.4207   $52.42   $52.40   $52.40  
  Purchase #2 $96.53   8.712%   $104.9397   $104.94   $104.95   $104.90  
  Purchase #3 $221.29   11.625%   $247.015   $247.02   $247.00   $247.00  
  Purchase #4 $221.26   4.175%   $230.4976   $230.50   $230.50   $230.50  
  Purchase #5 $237.57   6.775%   $253.6654   $253.67   $253.65   $253.70  
  Purchase #6 $164.65   9.481%   $180.2605   $180.26   $180.25   $180.30  
  Purchase #7 $183.64   11.186%   $204.182   $204.18   $204.20   $204.20  
  7 purchase totals = $1,171.62       $1,272.9809   $1,272.99   $1,272.95   $1,273.00