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 $58.91   6.120%   $62.5153   $62.52   $62.50   $62.50  
  Purchase #2 $206.72   5.622%   $218.3418   $218.34   $218.35   $218.30  
  Purchase #3 $241.83   5.632%   $255.4499   $255.45   $255.45   $255.40  
  Purchase #4 $246.47   5.152%   $259.1681   $259.17   $259.15   $259.20  
  Purchase #5 $139.83   7.258%   $149.9789   $149.98   $150.00   $150.00  
  Purchase #6 $230.69   6.425%   $245.5118   $245.51   $245.50   $245.50  
  Purchase #7 $166.42   6.664%   $177.5102   $177.51   $177.50   $177.50  
  7 purchase totals = $1,290.87       $1,368.4760   $1,368.48   $1,368.45   $1,368.40