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 $44.33   8.226%   $47.9766   $47.98   $48.00   $48.00  
  Purchase #2 $238.63   6.406%   $253.9166   $253.92   $253.90   $253.90  
  Purchase #3 $62.60   3.689%   $64.9093   $64.91   $64.90   $64.90  
  Purchase #4 $70.53   9.604%   $77.3037   $77.30   $77.30   $77.30  
  Purchase #5 $122.26   9.856%   $134.3099   $134.31   $134.30   $134.30  
  Purchase #6 $92.64   11.388%   $103.1898   $103.19   $103.20   $103.20  
  Purchase #7 $16.63   5.720%   $17.5812   $17.58   $17.60   $17.60  
  7 purchase totals = $647.62       $699.1871   $699.19   $699.20   $699.20