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	$127.41	3.364%	$131.6961	$131.70	$131.70	$131.70
Purchase #2	$120.72	9.198%	$131.8238	$131.82	$131.80	$131.80
Purchase #3	$71.69	9.406%	$78.4332	$78.43	$78.45	$78.40
Purchase #4	$121.29	3.366%	$125.3726	$125.37	$125.35	$125.40
Purchase #5	$238.28	10.431%	$263.135	$263.14	$263.15	$263.10
Purchase #6	$62.97	6.668%	$67.1688	$67.17	$67.15	$67.20
Purchase #7	$56.64	5.690%	$59.8628	$59.86	$59.85	$59.90
7 purchase totals =	$799.00		$857.4923	$857.49	$857.45	$857.50