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	$209.60	9.539%	$229.5937	$229.59	$229.60	$229.60
Purchase #2	$113.87	9.786%	$125.0133	$125.01	$125.00	$125.00
Purchase #3	$82.39	11.533%	$91.892	$91.89	$91.90	$91.90
Purchase #4	$147.78	5.394%	$155.7513	$155.75	$155.75	$155.80
Purchase #5	$105.96	4.315%	$110.5322	$110.53	$110.55	$110.50
Purchase #6	$18.27	9.671%	$20.0369	$20.04	$20.05	$20.00
Purchase #7	$113.44	8.748%	$123.3637	$123.36	$123.35	$123.40
7 purchase totals =	$791.31		$856.1831	$856.17	$856.20	$856.20