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	$98.86	3.647%	$102.4654	$102.47	$102.45	$102.50
Purchase #2	$141.94	12.400%	$159.5406	$159.54	$159.55	$159.50
Purchase #3	$148.47	7.668%	$159.8547	$159.85	$159.85	$159.90
Purchase #4	$198.92	12.356%	$223.4986	$223.50	$223.50	$223.50
Purchase #5	$182.59	3.369%	$188.7415	$188.74	$188.75	$188.70
Purchase #6	$100.30	4.454%	$104.7674	$104.77	$104.75	$104.80
Purchase #7	$129.80	12.664%	$146.2379	$146.24	$146.25	$146.20
7 purchase totals =	$1,000.88		$1,085.1061	$1,085.11	$1,085.10	$1,085.10