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	$153.33	11.754%	$171.3524	$171.35	$171.35	$171.40
Purchase #2	$93.27	13.253%	$105.6311	$105.63	$105.65	$105.60
Purchase #3	$165.63	3.695%	$171.75	$171.75	$171.75	$171.80
Purchase #4	$36.85	4.669%	$38.5705	$38.57	$38.55	$38.60
Purchase #5	$36.50	11.410%	$40.6647	$40.66	$40.65	$40.70
Purchase #6	$148.75	4.729%	$155.7844	$155.78	$155.80	$155.80
Purchase #7	$53.67	3.477%	$55.5361	$55.54	$55.55	$55.50
7 purchase totals =	$688.00		$739.2892	$739.28	$739.30	$739.40