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	$88.89	3.846%	$92.3087	$92.31	$92.30	$92.30
Purchase #2	$226.36	9.220%	$247.2304	$247.23	$247.25	$247.20
Purchase #3	$133.51	12.538%	$150.2495	$150.25	$150.25	$150.20
Purchase #4	$57.64	6.736%	$61.5226	$61.52	$61.50	$61.50
Purchase #5	$30.65	10.111%	$33.749	$33.75	$33.75	$33.70
Purchase #6	$61.35	10.204%	$67.6102	$67.61	$67.60	$67.60
Purchase #7	$8.34	3.131%	$8.6011	$8.60	$8.60	$8.60
7 purchase totals =	$606.74		$661.2715	$661.27	$661.25	$661.10