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 $58.66   3.872%   $60.9313   $60.93   $60.95   $60.90  
  Purchase #2 $75.26   4.594%   $78.7174   $78.72   $78.70   $78.70  
  Purchase #3 $209.61   5.621%   $221.3922   $221.39   $221.40   $221.40  
  Purchase #4 $191.26   4.551%   $199.9642   $199.96   $199.95   $200.00  
  Purchase #5 $247.79   8.495%   $268.8398   $268.84   $268.85   $268.80  
  Purchase #6 $57.96   10.438%   $64.0099   $64.01   $64.00   $64.00  
  Purchase #7 $77.71   10.445%   $85.8268   $85.83   $85.85   $85.80  
  7 purchase totals = $918.25       $979.6816   $979.68   $979.70   $979.60