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 $47.65   4.206%   $49.6542   $49.65   $49.65   $49.70  
  Purchase #2 $237.69   10.536%   $262.733   $262.73   $262.75   $262.70  
  Purchase #3 $102.35   13.671%   $116.3423   $116.34   $116.35   $116.30  
  Purchase #4 $18.40   5.821%   $19.4711   $19.47   $19.45   $19.50  
  Purchase #5 $218.92   7.150%   $234.5728   $234.57   $234.55   $234.60  
  Purchase #6 $180.95   11.866%   $202.4215   $202.42   $202.40   $202.40  
  Purchase #7 $39.33   3.395%   $40.6653   $40.67   $40.65   $40.70  
  7 purchase totals = $845.29       $925.8602   $925.85   $925.80   $925.90