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 $206.52   8.194%   $223.4422   $223.44   $223.45   $223.40  
  Purchase #2 $244.47   3.153%   $252.1781   $252.18   $252.20   $252.20  
  Purchase #3 $240.91   12.781%   $271.7007   $271.70   $271.70   $271.70  
  Purchase #4 $127.76   9.465%   $139.8525   $139.85   $139.85   $139.90  
  Purchase #5 $117.57   11.812%   $131.4574   $131.46   $131.45   $131.50  
  Purchase #6 $91.57   5.417%   $96.5303   $96.53   $96.55   $96.50  
  Purchase #7 $199.30   12.630%   $224.4716   $224.47   $224.45   $224.50  
  7 purchase totals = $1,228.10       $1,339.6328   $1,339.63   $1,339.65   $1,339.70