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	$247.89	13.732%	$281.9303	$281.93	$281.95	$281.90
Purchase #2	$223.94	5.623%	$236.5321	$236.53	$236.55	$236.50
Purchase #3	$56.29	9.736%	$61.7704	$61.77	$61.75	$61.80
Purchase #4	$88.29	3.203%	$91.1179	$91.12	$91.10	$91.10
Purchase #5	$175.46	3.254%	$181.1695	$181.17	$181.15	$181.20
Purchase #6	$78.82	5.189%	$82.91	$82.91	$82.90	$82.90
Purchase #7	$53.98	3.479%	$55.858	$55.86	$55.85	$55.90
7 purchase totals =	$924.67		$991.2882	$991.29	$991.25	$991.30