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	$69.67	13.867%	$79.3311	$79.33	$79.35	$79.30
Purchase #2	$99.63	13.519%	$113.099	$113.10	$113.10	$113.10
Purchase #3	$127.39	9.145%	$139.0398	$139.04	$139.05	$139.00
Purchase #4	$84.63	5.697%	$89.4514	$89.45	$89.45	$89.50
Purchase #5	$123.53	6.145%	$131.1209	$131.12	$131.10	$131.10
Purchase #6	$201.77	10.838%	$223.6378	$223.64	$223.65	$223.60
Purchase #7	$88.44	11.525%	$98.6327	$98.63	$98.65	$98.60
7 purchase totals =	$795.06		$874.3127	$874.31	$874.35	$874.20