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 $192.73   7.282%   $206.7646   $206.76   $206.75   $206.80  
  Purchase #2 $155.51   4.669%   $162.7708   $162.77   $162.75   $162.80  
  Purchase #3 $22.36   10.569%   $24.7232   $24.72   $24.70   $24.70  
  Purchase #4 $25.54   6.225%   $27.1299   $27.13   $27.15   $27.10  
  Purchase #5 $213.46   12.642%   $240.4456   $240.45   $240.45   $240.40  
  Purchase #6 $209.64   9.464%   $229.4803   $229.48   $229.50   $229.50  
  Purchase #7 $164.70   11.640%   $183.8711   $183.87   $183.85   $183.90  
  7 purchase totals = $983.94       $1,075.1855   $1,075.18   $1,075.15   $1,075.20