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 $188.93   9.347%   $206.5893   $206.59   $206.60   $206.60  
  Purchase #2 $94.42   12.458%   $106.1828   $106.18   $106.20   $106.20  
  Purchase #3 $47.25   10.544%   $52.232   $52.23   $52.25   $52.20  
  Purchase #4 $116.87   6.121%   $124.0236   $124.02   $124.00   $124.00  
  Purchase #5 $45.73   5.548%   $48.2671   $48.27   $48.25   $48.30  
  Purchase #6 $159.82   11.287%   $177.8589   $177.86   $177.85   $177.90  
  Purchase #7 $140.65   5.136%   $147.8738   $147.87   $147.85   $147.90  
  7 purchase totals = $793.67       $863.0275   $863.02   $863.00   $863.10