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	$113.66	6.361%	$120.8899	$120.89	$120.90	$120.90
Purchase #2	$209.77	13.540%	$238.1729	$238.17	$238.15	$238.20
Purchase #3	$190.85	10.328%	$210.561	$210.56	$210.55	$210.60
Purchase #4	$84.32	6.753%	$90.0141	$90.01	$90.00	$90.00
Purchase #5	$216.76	13.465%	$245.9467	$245.95	$245.95	$245.90
Purchase #6	$187.59	12.551%	$211.1344	$211.13	$211.15	$211.10
Purchase #7	$10.83	8.192%	$11.7172	$11.72	$11.70	$11.70
7 purchase totals =	$1,013.78		$1,128.4362	$1,128.43	$1,128.40	$1,128.40