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 $195.68   4.261%   $204.0179   $204.02   $204.00   $204.00  
  Purchase #2 $81.66   7.572%   $87.8433   $87.84   $87.85   $87.80  
  Purchase #3 $99.71   4.230%   $103.9277   $103.93   $103.95   $103.90  
  Purchase #4 $157.32   7.464%   $169.0624   $169.06   $169.05   $169.10  
  Purchase #5 $221.71   13.791%   $252.286   $252.29   $252.30   $252.30  
  Purchase #6 $225.95   11.247%   $251.3626   $251.36   $251.35   $251.40  
  Purchase #7 $6.86   8.138%   $7.4183   $7.42   $7.40   $7.40  
  7 purchase totals = $988.89       $1,075.9182   $1,075.92   $1,075.90   $1,075.90