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 $244.80   12.200%   $274.6656   $274.67   $274.65   $274.70  
  Purchase #2 $242.52   9.450%   $265.4381   $265.44   $265.45   $265.40  
  Purchase #3 $23.33   3.542%   $24.1563   $24.16   $24.15   $24.20  
  Purchase #4 $245.91   5.614%   $259.7154   $259.72   $259.70   $259.70  
  Purchase #5 $74.38   7.260%   $79.78   $79.78   $79.80   $79.80  
  Purchase #6 $51.72   12.165%   $58.0117   $58.01   $58.00   $58.00  
  Purchase #7 $101.72   5.149%   $106.9576   $106.96   $106.95   $107.00  
  7 purchase totals = $984.38       $1,068.7247   $1,068.74   $1,068.70   $1,068.80