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	$84.54	5.592%	$89.2675	$89.27	$89.25	$89.30
Purchase #2	$140.68	7.578%	$151.3407	$151.34	$151.35	$151.30
Purchase #3	$214.77	11.542%	$239.5588	$239.56	$239.55	$239.60
Purchase #4	$169.62	7.155%	$181.7563	$181.76	$181.75	$181.80
Purchase #5	$243.71	4.700%	$255.1644	$255.16	$255.15	$255.20
Purchase #6	$194.44	11.253%	$216.3203	$216.32	$216.30	$216.30
Purchase #7	$142.39	4.319%	$148.5398	$148.54	$148.55	$148.50
7 purchase totals =	$1,190.15		$1,281.9478	$1,281.95	$1,281.90	$1,282.00