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	$218.90	4.705%	$229.1992	$229.20	$229.20	$229.20
Purchase #2	$210.58	13.181%	$238.3365	$238.34	$238.35	$238.30
Purchase #3	$190.85	4.858%	$200.1215	$200.12	$200.10	$200.10
Purchase #4	$5.78	6.452%	$6.1529	$6.15	$6.15	$6.20
Purchase #5	$51.33	6.473%	$54.6526	$54.65	$54.65	$54.70
Purchase #6	$34.39	9.157%	$37.5391	$37.54	$37.55	$37.50
Purchase #7	$88.56	3.679%	$91.8181	$91.82	$91.80	$91.80
7 purchase totals =	$800.39		$857.8199	$857.82	$857.80	$857.80