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	$126.34	4.616%	$132.1719	$132.17	$132.15	$132.20
Purchase #2	$194.56	10.639%	$215.2592	$215.26	$215.25	$215.30
Purchase #3	$144.84	9.164%	$158.1131	$158.11	$158.10	$158.10
Purchase #4	$84.85	5.300%	$89.3471	$89.35	$89.35	$89.30
Purchase #5	$247.69	6.871%	$264.7088	$264.71	$264.70	$264.70
Purchase #6	$201.82	9.665%	$221.3259	$221.33	$221.35	$221.30
Purchase #7	$29.91	13.725%	$34.0151	$34.02	$34.00	$34.00
7 purchase totals =	$1,030.01		$1,114.9411	$1,114.95	$1,114.90	$1,114.90