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	$153.82	11.525%	$171.5478	$171.55	$171.55	$171.50
Purchase #2	$55.74	13.184%	$63.0888	$63.09	$63.10	$63.10
Purchase #3	$126.30	10.479%	$139.535	$139.54	$139.55	$139.50
Purchase #4	$31.63	4.467%	$33.0429	$33.04	$33.05	$33.00
Purchase #5	$146.47	5.254%	$154.1655	$154.17	$154.15	$154.20
Purchase #6	$168.44	9.501%	$184.4435	$184.44	$184.45	$184.40
Purchase #7	$42.61	6.860%	$45.533	$45.53	$45.55	$45.50
7 purchase totals =	$725.01		$791.3565	$791.36	$791.40	$791.20