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	$161.32	4.870%	$169.1763	$169.18	$169.20	$169.20
Purchase #2	$209.52	7.151%	$224.5028	$224.50	$224.50	$224.50
Purchase #3	$92.27	4.310%	$96.2468	$96.25	$96.25	$96.20
Purchase #4	$52.26	6.272%	$55.5377	$55.54	$55.55	$55.50
Purchase #5	$76.90	8.238%	$83.235	$83.24	$83.25	$83.20
Purchase #6	$38.64	5.253%	$40.6698	$40.67	$40.65	$40.70
Purchase #7	$150.79	9.680%	$165.3865	$165.39	$165.40	$165.40
7 purchase totals =	$781.70		$834.7549	$834.77	$834.80	$834.70