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 $70.63   4.679%   $73.9348   $73.93   $73.95   $73.90  
  Purchase #2 $211.30   5.253%   $222.3996   $222.40   $222.40   $222.40  
  Purchase #3 $64.86   10.541%   $71.6969   $71.70   $71.70   $71.70  
  Purchase #4 $49.44   10.641%   $54.7009   $54.70   $54.70   $54.70  
  Purchase #5 $248.88   5.282%   $262.0258   $262.03   $262.05   $262.00  
  Purchase #6 $167.69   8.667%   $182.2237   $182.22   $182.20   $182.20  
  Purchase #7 $110.88   8.717%   $120.5454   $120.55   $120.55   $120.50  
  7 purchase totals = $923.68       $987.5271   $987.53   $987.55   $987.40