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 $247.27   13.117%   $279.7044   $279.70   $279.70   $279.70  
  Purchase #2 $200.81   8.564%   $218.0074   $218.01   $218.00   $218.00  
  Purchase #3 $23.92   3.846%   $24.84   $24.84   $24.85   $24.80  
  Purchase #4 $246.33   5.669%   $260.2944   $260.29   $260.30   $260.30  
  Purchase #5 $232.83   13.169%   $263.4914   $263.49   $263.50   $263.50  
  Purchase #6 $47.85   12.688%   $53.9212   $53.92   $53.90   $53.90  
  Purchase #7 $12.58   12.717%   $14.1798   $14.18   $14.20   $14.20  
  7 purchase totals = $1,011.59       $1,114.4386   $1,114.43   $1,114.45   $1,114.40