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	$19.75	3.595%	$20.46	$20.46	$20.45	$20.50
Purchase #2	$196.36	13.656%	$223.1749	$223.17	$223.15	$223.20
Purchase #3	$191.38	13.516%	$217.2469	$217.25	$217.25	$217.20
Purchase #4	$28.88	13.849%	$32.8796	$32.88	$32.90	$32.90
Purchase #5	$245.68	12.343%	$276.0043	$276.00	$276.00	$276.00
Purchase #6	$106.93	5.386%	$112.6892	$112.69	$112.70	$112.70
Purchase #7	$67.73	4.651%	$70.8801	$70.88	$70.90	$70.90
7 purchase totals =	$856.71		$953.3350	$953.33	$953.35	$953.40