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	$242.52	5.259%	$255.2741	$255.27	$255.25	$255.30
Purchase #2	$5.89	4.634%	$6.1629	$6.16	$6.15	$6.20
Purchase #3	$50.48	10.680%	$55.8713	$55.87	$55.85	$55.90
Purchase #4	$51.44	4.121%	$53.5598	$53.56	$53.55	$53.60
Purchase #5	$162.29	12.682%	$182.8716	$182.87	$182.85	$182.90
Purchase #6	$83.27	12.190%	$93.4206	$93.42	$93.40	$93.40
Purchase #7	$140.42	8.757%	$152.7166	$152.72	$152.70	$152.70
7 purchase totals =	$736.31		$799.8769	$799.87	$799.75	$800.00