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	$71.90	12.235%	$80.697	$80.70	$80.70	$80.70
Purchase #2	$90.60	6.124%	$96.1483	$96.15	$96.15	$96.10
Purchase #3	$213.96	7.438%	$229.8743	$229.87	$229.85	$229.90
Purchase #4	$248.58	13.336%	$281.7306	$281.73	$281.75	$281.70
Purchase #5	$195.54	11.700%	$218.4182	$218.42	$218.40	$218.40
Purchase #6	$128.61	12.610%	$144.8277	$144.83	$144.85	$144.80
Purchase #7	$87.55	13.837%	$99.6643	$99.66	$99.65	$99.70
7 purchase totals =	$1,036.74		$1,151.3604	$1,151.36	$1,151.35	$1,151.30