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	$149.61	11.678%	$167.0815	$167.08	$167.10	$167.10
Purchase #2	$245.79	13.447%	$278.8414	$278.84	$278.85	$278.80
Purchase #3	$83.52	8.363%	$90.5048	$90.50	$90.50	$90.50
Purchase #4	$242.37	11.108%	$269.2925	$269.29	$269.30	$269.30
Purchase #5	$58.28	6.146%	$61.8619	$61.86	$61.85	$61.90
Purchase #6	$45.96	11.481%	$51.2367	$51.24	$51.25	$51.20
Purchase #7	$32.89	13.757%	$37.4147	$37.41	$37.40	$37.40
7 purchase totals =	$858.42		$956.2335	$956.22	$956.25	$956.20