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 $192.89   7.874%   $208.0782   $208.08   $208.10   $208.10  
  Purchase #2 $23.39   8.141%   $25.2942   $25.29   $25.30   $25.30  
  Purchase #3 $87.37   7.604%   $94.0136   $94.01   $94.00   $94.00  
  Purchase #4 $125.69   3.300%   $129.8378   $129.84   $129.85   $129.80  
  Purchase #5 $74.72   8.358%   $80.9651   $80.97   $80.95   $81.00  
  Purchase #6 $163.82   9.711%   $179.7286   $179.73   $179.75   $179.70  
  Purchase #7 $197.77   8.612%   $214.802   $214.80   $214.80   $214.80  
  7 purchase totals = $865.65       $932.7195   $932.72   $932.75   $932.70