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	$49.53	9.267%	$54.1199	$54.12	$54.10	$54.10
Purchase #2	$199.34	9.334%	$217.9464	$217.95	$217.95	$217.90
Purchase #3	$128.30	5.467%	$135.3142	$135.31	$135.30	$135.30
Purchase #4	$117.33	8.147%	$126.8889	$126.89	$126.90	$126.90
Purchase #5	$82.34	10.780%	$91.2163	$91.22	$91.20	$91.20
Purchase #6	$68.37	12.196%	$76.7084	$76.71	$76.70	$76.70
Purchase #7	$78.31	13.861%	$89.1645	$89.16	$89.15	$89.20
7 purchase totals =	$723.52		$791.3586	$791.36	$791.30	$791.30