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	$246.78	10.851%	$273.5581	$273.56	$273.55	$273.60
Purchase #2	$82.70	9.471%	$90.5325	$90.53	$90.55	$90.50
Purchase #3	$66.39	10.185%	$73.1518	$73.15	$73.15	$73.20
Purchase #4	$238.53	11.747%	$266.5501	$266.55	$266.55	$266.60
Purchase #5	$217.87	9.478%	$238.5197	$238.52	$238.50	$238.50
Purchase #6	$50.64	7.427%	$54.401	$54.40	$54.40	$54.40
Purchase #7	$246.29	7.283%	$264.2273	$264.23	$264.25	$264.20
7 purchase totals =	$1,149.20		$1,260.9405	$1,260.94	$1,260.95	$1,261.00