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	$185.41	4.763%	$194.2411	$194.24	$194.25	$194.20
Purchase #2	$72.78	9.180%	$79.4612	$79.46	$79.45	$79.50
Purchase #3	$35.31	12.807%	$39.8322	$39.83	$39.85	$39.80
Purchase #4	$150.36	12.350%	$168.9295	$168.93	$168.95	$168.90
Purchase #5	$65.60	9.523%	$71.8471	$71.85	$71.85	$71.80
Purchase #6	$41.37	9.233%	$45.1897	$45.19	$45.20	$45.20
Purchase #7	$57.98	4.160%	$60.392	$60.39	$60.40	$60.40
7 purchase totals =	$608.81		$659.8928	$659.89	$659.95	$659.80