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 $60.90   6.758%   $65.0156   $65.02   $65.00   $65.00  
  Purchase #2 $224.31   7.283%   $240.6465   $240.65   $240.65   $240.60  
  Purchase #3 $25.63   9.419%   $28.0441   $28.04   $28.05   $28.00  
  Purchase #4 $8.48   5.505%   $8.9468   $8.95   $8.95   $8.90  
  Purchase #5 $83.52   13.738%   $94.994   $94.99   $95.00   $95.00  
  Purchase #6 $191.59   8.394%   $207.6721   $207.67   $207.65   $207.70  
  Purchase #7 $70.89   6.676%   $75.6226   $75.62   $75.60   $75.60  
  7 purchase totals = $665.32       $720.9417   $720.94   $720.90   $720.80