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 $55.37   5.582%   $58.4608   $58.46   $58.45   $58.50  
  Purchase #2 $126.54   12.557%   $142.4296   $142.43   $142.45   $142.40  
  Purchase #3 $216.47   7.596%   $232.9131   $232.91   $232.90   $232.90  
  Purchase #4 $241.44   5.422%   $254.5309   $254.53   $254.55   $254.50  
  Purchase #5 $160.28   7.618%   $172.4901   $172.49   $172.50   $172.50  
  Purchase #6 $186.97   10.664%   $206.9085   $206.91   $206.90   $206.90  
  Purchase #7 $176.78   10.799%   $195.8705   $195.87   $195.85   $195.90  
  7 purchase totals = $1,163.85       $1,263.6035   $1,263.60   $1,263.60   $1,263.60