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	$69.38	6.519%	$73.9029	$73.90	$73.90	$73.90
Purchase #2	$200.70	7.414%	$215.5799	$215.58	$215.60	$215.60
Purchase #3	$142.54	11.749%	$159.287	$159.29	$159.30	$159.30
Purchase #4	$52.91	3.288%	$54.6497	$54.65	$54.65	$54.60
Purchase #5	$177.54	12.740%	$200.1586	$200.16	$200.15	$200.20
Purchase #6	$98.62	6.315%	$104.8479	$104.85	$104.85	$104.80
Purchase #7	$18.26	12.330%	$20.5115	$20.51	$20.50	$20.50
7 purchase totals =	$759.95		$828.9375	$828.94	$828.95	$828.90