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 $202.66   9.818%   $222.5572   $222.56   $222.55   $222.60  
  Purchase #2 $223.44   8.696%   $242.8703   $242.87   $242.85   $242.90  
  Purchase #3 $53.38   5.428%   $56.2775   $56.28   $56.30   $56.30  
  Purchase #4 $96.70   8.161%   $104.5917   $104.59   $104.60   $104.60  
  Purchase #5 $228.61   6.666%   $243.8491   $243.85   $243.85   $243.80  
  Purchase #6 $206.87   5.367%   $217.9727   $217.97   $217.95   $218.00  
  Purchase #7 $196.71   9.655%   $215.7024   $215.70   $215.70   $215.70  
  7 purchase totals = $1,208.37       $1,303.8209   $1,303.82   $1,303.80   $1,303.90