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	$132.38	6.345%	$140.7795	$140.78	$140.80	$140.80
Purchase #2	$146.75	12.517%	$165.1187	$165.12	$165.10	$165.10
Purchase #3	$142.70	13.805%	$162.3997	$162.40	$162.40	$162.40
Purchase #4	$170.50	6.238%	$181.1358	$181.14	$181.15	$181.10
Purchase #5	$110.55	12.121%	$123.9498	$123.95	$123.95	$123.90
Purchase #6	$53.62	6.110%	$56.8962	$56.90	$56.90	$56.90
Purchase #7	$243.37	11.129%	$270.4546	$270.45	$270.45	$270.50
7 purchase totals =	$999.87		$1,100.7343	$1,100.74	$1,100.75	$1,100.70