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 $186.91   11.459%   $208.328   $208.33   $208.35   $208.30  
  Purchase #2 $230.84   12.625%   $259.9836   $259.98   $260.00   $260.00  
  Purchase #3 $12.59   13.476%   $14.2866   $14.29   $14.30   $14.30  
  Purchase #4 $54.61   8.431%   $59.2142   $59.21   $59.20   $59.20  
  Purchase #5 $227.54   5.776%   $240.6827   $240.68   $240.70   $240.70  
  Purchase #6 $166.38   5.459%   $175.4627   $175.46   $175.45   $175.50  
  Purchase #7 $12.42   11.364%   $13.8314   $13.83   $13.85   $13.80  
  7 purchase totals = $891.29       $971.7892   $971.78   $971.85   $971.80