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 $216.37   3.374%   $223.6703   $223.67   $223.65   $223.70  
  Purchase #2 $182.48   5.393%   $192.3211   $192.32   $192.30   $192.30  
  Purchase #3 $32.71   8.537%   $35.5025   $35.50   $35.50   $35.50  
  Purchase #4 $119.60   9.634%   $131.1223   $131.12   $131.10   $131.10  
  Purchase #5 $232.95   9.381%   $254.803   $254.80   $254.80   $254.80  
  Purchase #6 $235.43   4.617%   $246.2998   $246.30   $246.30   $246.30  
  Purchase #7 $197.80   5.581%   $208.8392   $208.84   $208.85   $208.80  
  7 purchase totals = $1,217.34       $1,292.5582   $1,292.55   $1,292.50   $1,292.50