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 $32.77   10.489%   $36.2072   $36.21   $36.20   $36.20  
  Purchase #2 $119.57   11.841%   $133.7283   $133.73   $133.75   $133.70  
  Purchase #3 $166.25   3.466%   $172.0122   $172.01   $172.00   $172.00  
  Purchase #4 $226.27   10.667%   $250.4062   $250.41   $250.40   $250.40  
  Purchase #5 $184.76   4.594%   $193.2479   $193.25   $193.25   $193.20  
  Purchase #6 $184.43   12.255%   $207.0319   $207.03   $207.05   $207.00  
  Purchase #7 $246.77   7.525%   $265.3394   $265.34   $265.35   $265.30  
  7 purchase totals = $1,160.82       $1,257.9731   $1,257.98   $1,258.00   $1,257.80