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 $62.86   5.352%   $66.2243   $66.22   $66.20   $66.20  
  Purchase #2 $193.74   3.829%   $201.1583   $201.16   $201.15   $201.20  
  Purchase #3 $115.76   6.607%   $123.4083   $123.41   $123.40   $123.40  
  Purchase #4 $114.88   9.438%   $125.7224   $125.72   $125.70   $125.70  
  Purchase #5 $51.80   7.539%   $55.7052   $55.71   $55.70   $55.70  
  Purchase #6 $180.35   6.482%   $192.0403   $192.04   $192.05   $192.00  
  Purchase #7 $21.86   3.277%   $22.5764   $22.58   $22.60   $22.60  
  7 purchase totals = $741.25       $786.8352   $786.84   $786.80   $786.80