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	$113.55	13.310%	$128.6635	$128.66	$128.65	$128.70
Purchase #2	$84.83	13.586%	$96.355	$96.36	$96.35	$96.40
Purchase #3	$14.54	11.849%	$16.2628	$16.26	$16.25	$16.30
Purchase #4	$181.38	4.782%	$190.0536	$190.05	$190.05	$190.10
Purchase #5	$29.78	7.818%	$32.1082	$32.11	$32.10	$32.10
Purchase #6	$136.63	10.596%	$151.1073	$151.11	$151.10	$151.10
Purchase #7	$46.90	13.511%	$53.2367	$53.24	$53.25	$53.20
7 purchase totals =	$607.61		$667.7871	$667.79	$667.75	$667.90