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 $69.57   4.847%   $72.9421   $72.94   $72.95   $72.90  
  Purchase #2 $232.95   11.357%   $259.4061   $259.41   $259.40   $259.40  
  Purchase #3 $199.39   8.328%   $215.9952   $216.00   $216.00   $216.00  
  Purchase #4 $203.31   4.608%   $212.6785   $212.68   $212.70   $212.70  
  Purchase #5 $65.34   5.567%   $68.9775   $68.98   $69.00   $69.00  
  Purchase #6 $45.74   4.236%   $47.6775   $47.68   $47.70   $47.70  
  Purchase #7 $30.68   11.399%   $34.1772   $34.18   $34.20   $34.20  
  7 purchase totals = $846.98       $911.8541   $911.87   $911.95   $911.90