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 $59.95   10.470%   $66.2268   $66.23   $66.25   $66.20  
  Purchase #2 $245.48   7.844%   $264.7355   $264.74   $264.75   $264.70  
  Purchase #3 $123.42   3.678%   $127.9594   $127.96   $127.95   $128.00  
  Purchase #4 $215.85   8.387%   $233.9533   $233.95   $233.95   $234.00  
  Purchase #5 $52.69   6.859%   $56.304   $56.30   $56.30   $56.30  
  Purchase #6 $56.72   3.306%   $58.5952   $58.60   $58.60   $58.60  
  Purchase #7 $8.52   7.209%   $9.1342   $9.13   $9.15   $9.10  
  7 purchase totals = $762.63       $816.9084   $816.91   $816.95   $816.90