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	$19.53	3.790%	$20.2702	$20.27	$20.25	$20.30
Purchase #2	$36.33	11.654%	$40.5639	$40.56	$40.55	$40.60
Purchase #3	$208.86	4.573%	$218.4112	$218.41	$218.40	$218.40
Purchase #4	$215.54	3.616%	$223.3339	$223.33	$223.35	$223.30
Purchase #5	$52.51	3.334%	$54.2607	$54.26	$54.25	$54.30
Purchase #6	$51.80	6.760%	$55.3017	$55.30	$55.30	$55.30
Purchase #7	$107.66	13.753%	$122.4665	$122.47	$122.45	$122.50
7 purchase totals =	$692.23		$734.6081	$734.60	$734.55	$734.70