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	$133.85	12.468%	$150.5384	$150.54	$150.55	$150.50
Purchase #2	$232.74	13.240%	$263.5548	$263.55	$263.55	$263.60
Purchase #3	$90.52	10.229%	$99.7793	$99.78	$99.80	$99.80
Purchase #4	$221.27	7.663%	$238.2259	$238.23	$238.25	$238.20
Purchase #5	$112.66	10.655%	$124.6639	$124.66	$124.65	$124.70
Purchase #6	$172.38	10.184%	$189.9352	$189.94	$189.95	$189.90
Purchase #7	$172.73	3.383%	$178.5735	$178.57	$178.55	$178.60
7 purchase totals =	$1,136.15		$1,245.2710	$1,245.27	$1,245.30	$1,245.30