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 $70.82   4.347%   $73.8985   $73.90   $73.90   $73.90  
  Purchase #2 $88.63   11.376%   $98.7125   $98.71   $98.70   $98.70  
  Purchase #3 $131.86   5.116%   $138.606   $138.61   $138.60   $138.60  
  Purchase #4 $58.60   10.871%   $64.9704   $64.97   $64.95   $65.00  
  Purchase #5 $23.79   13.481%   $26.9971   $27.00   $27.00   $27.00  
  Purchase #6 $229.97   4.873%   $241.1764   $241.18   $241.20   $241.20  
  Purchase #7 $167.25   8.273%   $181.0866   $181.09   $181.10   $181.10  
  7 purchase totals = $770.92       $825.4475   $825.46   $825.45   $825.50