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	$85.50	3.107%	$88.1565	$88.16	$88.15	$88.20
Purchase #2	$32.46	3.323%	$33.5386	$33.54	$33.55	$33.50
Purchase #3	$230.30	12.121%	$258.2147	$258.21	$258.20	$258.20
Purchase #4	$178.52	10.251%	$196.8201	$196.82	$196.80	$196.80
Purchase #5	$141.87	3.801%	$147.2625	$147.26	$147.25	$147.30
Purchase #6	$84.60	8.645%	$91.9137	$91.91	$91.90	$91.90
Purchase #7	$26.32	9.599%	$28.8465	$28.85	$28.85	$28.80
7 purchase totals =	$779.57		$844.7526	$844.75	$844.70	$844.70