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 $214.47   12.391%   $241.045   $241.05   $241.05   $241.00  
  Purchase #2 $70.43   13.609%   $80.0148   $80.01   $80.00   $80.00  
  Purchase #3 $45.89   4.795%   $48.0904   $48.09   $48.10   $48.10  
  Purchase #4 $83.73   5.551%   $88.3779   $88.38   $88.40   $88.40  
  Purchase #5 $182.65   13.826%   $207.9032   $207.90   $207.90   $207.90  
  Purchase #6 $26.64   12.621%   $30.0022   $30.00   $30.00   $30.00  
  Purchase #7 $29.78   11.147%   $33.0996   $33.10   $33.10   $33.10  
  7 purchase totals = $653.59       $728.5331   $728.53   $728.55   $728.50