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 $57.46   4.304%   $59.9331   $59.93   $59.95   $59.90  
  Purchase #2 $143.29   10.690%   $158.6077   $158.61   $158.60   $158.60  
  Purchase #3 $214.30   9.396%   $234.4356   $234.44   $234.45   $234.40  
  Purchase #4 $38.64   8.292%   $41.844   $41.84   $41.85   $41.80  
  Purchase #5 $60.94   6.463%   $64.8786   $64.88   $64.90   $64.90  
  Purchase #6 $111.58   11.390%   $124.289   $124.29   $124.30   $124.30  
  Purchase #7 $60.64   9.490%   $66.3947   $66.39   $66.40   $66.40  
  7 purchase totals = $686.85       $750.3827   $750.38   $750.45   $750.30