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	$51.93	3.549%	$53.773	$53.77	$53.75	$53.80
Purchase #2	$209.48	5.130%	$220.2263	$220.23	$220.25	$220.20
Purchase #3	$55.27	7.146%	$59.2196	$59.22	$59.20	$59.20
Purchase #4	$115.85	6.414%	$123.2806	$123.28	$123.30	$123.30
Purchase #5	$151.48	13.299%	$171.6253	$171.63	$171.65	$171.60
Purchase #6	$240.90	3.714%	$249.847	$249.85	$249.85	$249.80
Purchase #7	$70.72	9.279%	$77.2821	$77.28	$77.30	$77.30
7 purchase totals =	$895.63		$955.2539	$955.26	$955.30	$955.20