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 $66.97   11.191%   $74.4646   $74.46   $74.45   $74.50  
  Purchase #2 $244.30   11.411%   $272.1771   $272.18   $272.20   $272.20  
  Purchase #3 $172.33   5.528%   $181.8564   $181.86   $181.85   $181.90  
  Purchase #4 $144.67   13.738%   $164.5448   $164.54   $164.55   $164.50  
  Purchase #5 $33.41   4.619%   $34.9532   $34.95   $34.95   $35.00  
  Purchase #6 $250.80   3.281%   $259.0287   $259.03   $259.05   $259.00  
  Purchase #7 $183.96   12.748%   $207.4112   $207.41   $207.40   $207.40  
  7 purchase totals = $1,096.44       $1,194.4360   $1,194.43   $1,194.45   $1,194.50