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	$242.87	12.617%	$273.5129	$273.51	$273.50	$273.50
Purchase #2	$32.99	8.795%	$35.8915	$35.89	$35.90	$35.90
Purchase #3	$204.53	9.169%	$223.2834	$223.28	$223.30	$223.30
Purchase #4	$167.38	6.424%	$178.1325	$178.13	$178.15	$178.10
Purchase #5	$57.55	6.835%	$61.4835	$61.48	$61.50	$61.50
Purchase #6	$67.75	11.233%	$75.3604	$75.36	$75.35	$75.40
Purchase #7	$202.32	8.399%	$219.3129	$219.31	$219.30	$219.30
7 purchase totals =	$975.39		$1,066.9771	$1,066.96	$1,067.00	$1,067.00