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	$100.70	9.803%	$110.5716	$110.57	$110.55	$110.60
Purchase #2	$206.98	9.129%	$225.8752	$225.88	$225.90	$225.90
Purchase #3	$46.81	13.820%	$53.2791	$53.28	$53.30	$53.30
Purchase #4	$41.52	5.305%	$43.7226	$43.72	$43.70	$43.70
Purchase #5	$37.33	9.430%	$40.8502	$40.85	$40.85	$40.90
Purchase #6	$205.94	7.621%	$221.6347	$221.63	$221.65	$221.60
Purchase #7	$88.45	7.731%	$95.2881	$95.29	$95.30	$95.30
7 purchase totals =	$727.73		$791.2215	$791.22	$791.25	$791.30