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	$174.46	6.375%	$185.5818	$185.58	$185.60	$185.60
Purchase #2	$238.82	12.223%	$268.011	$268.01	$268.00	$268.00
Purchase #3	$135.56	6.297%	$144.0962	$144.10	$144.10	$144.10
Purchase #4	$211.52	5.684%	$223.5428	$223.54	$223.55	$223.50
Purchase #5	$11.72	10.681%	$12.9718	$12.97	$12.95	$13.00
Purchase #6	$43.88	12.644%	$49.4282	$49.43	$49.45	$49.40
Purchase #7	$139.49	11.497%	$155.5272	$155.53	$155.55	$155.50
7 purchase totals =	$955.45		$1,039.1590	$1,039.16	$1,039.20	$1,039.10