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 $48.26   10.543%   $53.3481   $53.35   $53.35   $53.30  
  Purchase #2 $66.83   5.652%   $70.6072   $70.61   $70.60   $70.60  
  Purchase #3 $120.65   6.412%   $128.3861   $128.39   $128.40   $128.40  
  Purchase #4 $59.73   11.468%   $66.5798   $66.58   $66.60   $66.60  
  Purchase #5 $73.66   3.578%   $76.2956   $76.30   $76.30   $76.30  
  Purchase #6 $60.88   10.652%   $67.3649   $67.36   $67.35   $67.40  
  Purchase #7 $201.35   5.608%   $212.6417   $212.64   $212.65   $212.60  
  7 purchase totals = $631.36       $675.2234   $675.23   $675.25   $675.20