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	$33.64	11.634%	$37.5537	$37.55	$37.55	$37.60
Purchase #2	$96.27	7.324%	$103.3208	$103.32	$103.30	$103.30
Purchase #3	$65.90	6.428%	$70.1361	$70.14	$70.15	$70.10
Purchase #4	$96.64	7.624%	$104.0078	$104.01	$104.00	$104.00
Purchase #5	$35.38	8.373%	$38.3424	$38.34	$38.35	$38.30
Purchase #6	$191.36	13.227%	$216.6712	$216.67	$216.65	$216.70
Purchase #7	$243.92	10.289%	$269.0169	$269.02	$269.00	$269.00
7 purchase totals =	$763.11		$839.0489	$839.05	$839.00	$839.00