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 $216.86   9.402%   $237.2492   $237.25   $237.25   $237.20  
  Purchase #2 $148.98   4.491%   $155.6707   $155.67   $155.65   $155.70  
  Purchase #3 $18.32   4.823%   $19.2036   $19.20   $19.20   $19.20  
  Purchase #4 $101.72   13.619%   $115.5732   $115.57   $115.55   $115.60  
  Purchase #5 $225.60   13.511%   $256.0808   $256.08   $256.10   $256.10  
  Purchase #6 $15.85   9.109%   $17.2938   $17.29   $17.30   $17.30  
  Purchase #7 $228.90   12.687%   $257.9405   $257.94   $257.95   $257.90  
  7 purchase totals = $956.23       $1,059.0118   $1,059.00   $1,059.00   $1,059.00