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 $14.90   5.769%   $15.7596   $15.76   $15.75   $15.80  
  Purchase #2 $179.91   3.388%   $186.0054   $186.01   $186.00   $186.00  
  Purchase #3 $109.66   13.140%   $124.0693   $124.07   $124.05   $124.10  
  Purchase #4 $249.33   5.269%   $262.4672   $262.47   $262.45   $262.50  
  Purchase #5 $204.45   11.236%   $227.422   $227.42   $227.40   $227.40  
  Purchase #6 $86.68   9.615%   $95.0143   $95.01   $95.00   $95.00  
  Purchase #7 $201.46   7.421%   $216.4103   $216.41   $216.40   $216.40  
  7 purchase totals = $1,046.39       $1,127.1481   $1,127.15   $1,127.05   $1,127.20