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 $246.93   5.620%   $260.8075   $260.81   $260.80   $260.80  
  Purchase #2 $42.85   11.749%   $47.8844   $47.88   $47.90   $47.90  
  Purchase #3 $54.27   13.233%   $61.4515   $61.45   $61.45   $61.50  
  Purchase #4 $153.74   6.460%   $163.6716   $163.67   $163.65   $163.70  
  Purchase #5 $225.63   13.833%   $256.8414   $256.84   $256.85   $256.80  
  Purchase #6 $234.51   5.302%   $246.9437   $246.94   $246.95   $246.90  
  Purchase #7 $224.34   3.438%   $232.0528   $232.05   $232.05   $232.10  
  7 purchase totals = $1,182.27       $1,269.6529   $1,269.64   $1,269.65   $1,269.70