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 $112.92   11.108%   $125.4632   $125.46   $125.45   $125.50  
  Purchase #2 $52.34   13.736%   $59.5294   $59.53   $59.55   $59.50  
  Purchase #3 $52.91   5.857%   $56.0089   $56.01   $56.00   $56.00  
  Purchase #4 $62.42   7.579%   $67.1508   $67.15   $67.15   $67.20  
  Purchase #5 $65.29   6.624%   $69.6148   $69.61   $69.60   $69.60  
  Purchase #6 $167.94   8.403%   $182.052   $182.05   $182.05   $182.10  
  Purchase #7 $216.59   9.531%   $237.2332   $237.23   $237.25   $237.20  
  7 purchase totals = $730.41       $797.0523   $797.04   $797.05   $797.10