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	$172.57	8.364%	$187.0038	$187.00	$187.00	$187.00
Purchase #2	$95.75	11.674%	$106.9279	$106.93	$106.95	$106.90
Purchase #3	$142.71	11.539%	$159.1773	$159.18	$159.20	$159.20
Purchase #4	$181.68	10.370%	$200.5202	$200.52	$200.50	$200.50
Purchase #5	$153.59	13.521%	$174.3569	$174.36	$174.35	$174.40
Purchase #6	$164.29	12.616%	$185.0168	$185.02	$185.00	$185.00
Purchase #7	$30.56	9.285%	$33.3975	$33.40	$33.40	$33.40
7 purchase totals =	$941.15		$1,046.4004	$1,046.41	$1,046.40	$1,046.40