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	$35.45	5.530%	$37.4104	$37.41	$37.40	$37.40
Purchase #2	$72.73	6.327%	$77.3316	$77.33	$77.35	$77.30
Purchase #3	$221.55	7.121%	$237.3266	$237.33	$237.35	$237.30
Purchase #4	$131.86	12.613%	$148.4915	$148.49	$148.50	$148.50
Purchase #5	$43.55	6.360%	$46.3198	$46.32	$46.30	$46.30
Purchase #6	$245.56	13.813%	$279.4792	$279.48	$279.50	$279.50
Purchase #7	$21.54	3.220%	$22.2336	$22.23	$22.25	$22.20
7 purchase totals =	$772.24		$848.5927	$848.59	$848.65	$848.50