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 $118.47   10.746%   $131.2008   $131.20   $131.20   $131.20  
  Purchase #2 $49.29   9.377%   $53.9119   $53.91   $53.90   $53.90  
  Purchase #3 $249.95   4.202%   $260.4529   $260.45   $260.45   $260.50  
  Purchase #4 $98.54   11.615%   $109.9854   $109.99   $110.00   $110.00  
  Purchase #5 $115.94   6.557%   $123.5422   $123.54   $123.55   $123.50  
  Purchase #6 $169.44   13.401%   $192.1467   $192.15   $192.15   $192.10  
  Purchase #7 $111.48   13.710%   $126.7639   $126.76   $126.75   $126.80  
  7 purchase totals = $913.11       $998.0038   $998.00   $998.00   $998.00