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 $239.73   8.852%   $260.9509   $260.95   $260.95   $261.00  
  Purchase #2 $246.45   11.630%   $275.1121   $275.11   $275.10   $275.10  
  Purchase #3 $96.54   3.798%   $100.2066   $100.21   $100.20   $100.20  
  Purchase #4 $152.89   11.539%   $170.532   $170.53   $170.55   $170.50  
  Purchase #5 $76.48   5.790%   $80.9082   $80.91   $80.90   $80.90  
  Purchase #6 $126.52   5.794%   $133.8506   $133.85   $133.85   $133.90  
  Purchase #7 $21.81   6.483%   $23.2239   $23.22   $23.20   $23.20  
  7 purchase totals = $960.42       $1,044.7843   $1,044.78   $1,044.75   $1,044.80