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 $214.42   9.437%   $234.6548   $234.65   $234.65   $234.70  
  Purchase #2 $113.25   12.580%   $127.4969   $127.50   $127.50   $127.50  
  Purchase #3 $60.90   6.532%   $64.878   $64.88   $64.90   $64.90  
  Purchase #4 $32.77   4.269%   $34.169   $34.17   $34.15   $34.20  
  Purchase #5 $165.57   6.479%   $176.2973   $176.30   $176.30   $176.30  
  Purchase #6 $65.38   9.607%   $71.6611   $71.66   $71.65   $71.70  
  Purchase #7 $189.63   6.514%   $201.9825   $201.98   $202.00   $202.00  
  7 purchase totals = $841.92       $911.1396   $911.14   $911.15   $911.30