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 $88.74   11.288%   $98.757   $98.76   $98.75   $98.80  
  Purchase #2 $82.77   10.856%   $91.7555   $91.76   $91.75   $91.80  
  Purchase #3 $143.32   10.371%   $158.1837   $158.18   $158.20   $158.20  
  Purchase #4 $176.78   9.405%   $193.4062   $193.41   $193.40   $193.40  
  Purchase #5 $205.55   3.595%   $212.9395   $212.94   $212.95   $212.90  
  Purchase #6 $97.60   7.840%   $105.2518   $105.25   $105.25   $105.30  
  Purchase #7 $246.99   5.361%   $260.2311   $260.23   $260.25   $260.20  
  7 purchase totals = $1,041.75       $1,120.5248   $1,120.53   $1,120.55   $1,120.60