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	$37.75	13.850%	$42.9784	$42.98	$43.00	$43.00
Purchase #2	$154.49	8.610%	$167.7916	$167.79	$167.80	$167.80
Purchase #3	$244.39	5.613%	$258.1076	$258.11	$258.10	$258.10
Purchase #4	$6.76	8.615%	$7.3424	$7.34	$7.35	$7.30
Purchase #5	$27.27	6.655%	$29.0848	$29.08	$29.10	$29.10
Purchase #6	$216.98	11.539%	$242.0173	$242.02	$242.00	$242.00
Purchase #7	$116.53	5.799%	$123.2876	$123.29	$123.30	$123.30
7 purchase totals =	$804.17		$870.6097	$870.61	$870.65	$870.60