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	$37.90	12.695%	$42.7114	$42.71	$42.70	$42.70
Purchase #2	$107.86	10.287%	$118.9556	$118.96	$118.95	$119.00
Purchase #3	$91.69	8.319%	$99.3177	$99.32	$99.30	$99.30
Purchase #4	$45.58	4.348%	$47.5618	$47.56	$47.55	$47.60
Purchase #5	$37.34	8.109%	$40.3679	$40.37	$40.35	$40.40
Purchase #6	$83.59	3.255%	$86.3109	$86.31	$86.30	$86.30
Purchase #7	$227.65	5.554%	$240.2937	$240.29	$240.30	$240.30
7 purchase totals =	$631.61		$675.5190	$675.52	$675.45	$675.60