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 $68.73   4.606%   $71.8957   $71.90   $71.90   $71.90  
  Purchase #2 $184.85   13.846%   $210.4443   $210.44   $210.45   $210.40  
  Purchase #3 $146.34   7.266%   $156.9731   $156.97   $156.95   $157.00  
  Purchase #4 $151.95   11.514%   $169.4455   $169.45   $169.45   $169.40  
  Purchase #5 $123.38   8.589%   $133.9771   $133.98   $134.00   $134.00  
  Purchase #6 $121.55   3.829%   $126.2041   $126.20   $126.20   $126.20  
  Purchase #7 $163.50   3.143%   $168.6388   $168.64   $168.65   $168.60  
  7 purchase totals = $960.30       $1,037.5786   $1,037.58   $1,037.60   $1,037.50