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 $246.54   11.473%   $274.8255   $274.83   $274.85   $274.80  
  Purchase #2 $227.48   11.145%   $252.8326   $252.83   $252.85   $252.80  
  Purchase #3 $213.94   4.874%   $224.3674   $224.37   $224.35   $224.40  
  Purchase #4 $122.83   11.208%   $136.5968   $136.60   $136.60   $136.60  
  Purchase #5 $54.33   3.499%   $56.231   $56.23   $56.25   $56.20  
  Purchase #6 $11.76   5.122%   $12.3623   $12.36   $12.35   $12.40  
  Purchase #7 $84.57   4.648%   $88.5008   $88.50   $88.50   $88.50  
  7 purchase totals = $961.45       $1,045.7164   $1,045.72   $1,045.75   $1,045.70