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 $220.66   12.201%   $247.5827   $247.58   $247.60   $247.60  
  Purchase #2 $22.45   3.864%   $23.3175   $23.32   $23.30   $23.30  
  Purchase #3 $223.98   4.603%   $234.2898   $234.29   $234.30   $234.30  
  Purchase #4 $233.78   10.841%   $259.1241   $259.12   $259.10   $259.10  
  Purchase #5 $104.85   5.146%   $110.2456   $110.25   $110.25   $110.20  
  Purchase #6 $122.92   13.794%   $139.8756   $139.88   $139.90   $139.90  
  Purchase #7 $26.46   10.798%   $29.3172   $29.32   $29.30   $29.30  
  7 purchase totals = $955.10       $1,043.7525   $1,043.76   $1,043.75   $1,043.70