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 $218.85   6.255%   $232.5391   $232.54   $232.55   $232.50  
  Purchase #2 $139.96   8.575%   $151.9616   $151.96   $151.95   $152.00  
  Purchase #3 $245.36   6.799%   $262.042   $262.04   $262.05   $262.00  
  Purchase #4 $43.53   9.488%   $47.6601   $47.66   $47.65   $47.70  
  Purchase #5 $52.73   13.599%   $59.9008   $59.90   $59.90   $59.90  
  Purchase #6 $88.86   5.281%   $93.5527   $93.55   $93.55   $93.60  
  Purchase #7 $130.28   7.778%   $140.4132   $140.41   $140.40   $140.40  
  7 purchase totals = $919.57       $988.0695   $988.06   $988.05   $988.10