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	$187.40	6.685%	$199.9277	$199.93	$199.95	$199.90
Purchase #2	$244.73	13.341%	$277.3794	$277.38	$277.40	$277.40
Purchase #3	$142.94	13.226%	$161.8452	$161.85	$161.85	$161.80
Purchase #4	$60.80	11.688%	$67.9063	$67.91	$67.90	$67.90
Purchase #5	$226.63	10.443%	$250.297	$250.30	$250.30	$250.30
Purchase #6	$55.88	10.702%	$61.8603	$61.86	$61.85	$61.90
Purchase #7	$119.95	9.117%	$130.8858	$130.89	$130.90	$130.90
7 purchase totals =	$1,038.33		$1,150.1017	$1,150.12	$1,150.15	$1,150.10