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	$234.33	12.635%	$263.9376	$263.94	$263.95	$263.90
Purchase #2	$239.72	10.849%	$265.7272	$265.73	$265.75	$265.70
Purchase #3	$148.82	6.223%	$158.0811	$158.08	$158.10	$158.10
Purchase #4	$79.32	4.594%	$82.964	$82.96	$82.95	$83.00
Purchase #5	$157.86	10.843%	$174.9768	$174.98	$175.00	$175.00
Purchase #6	$33.96	8.609%	$36.8836	$36.88	$36.90	$36.90
Purchase #7	$106.31	10.259%	$117.2163	$117.22	$117.20	$117.20
7 purchase totals =	$1,000.32		$1,099.7866	$1,099.79	$1,099.85	$1,099.80