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 $210.84   10.796%   $233.6023   $233.60   $233.60   $233.60  
  Purchase #2 $119.76   11.597%   $133.6486   $133.65   $133.65   $133.60  
  Purchase #3 $15.82   9.423%   $17.3107   $17.31   $17.30   $17.30  
  Purchase #4 $240.57   7.115%   $257.6866   $257.69   $257.70   $257.70  
  Purchase #5 $193.30   6.267%   $205.4141   $205.41   $205.40   $205.40  
  Purchase #6 $119.46   4.624%   $124.9838   $124.98   $125.00   $125.00  
  Purchase #7 $182.75   9.306%   $199.7567   $199.76   $199.75   $199.80  
  7 purchase totals = $1,082.50       $1,172.4028   $1,172.40   $1,172.40   $1,172.40