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	$151.85	12.819%	$171.3157	$171.32	$171.30	$171.30
Purchase #2	$226.41	8.258%	$245.1069	$245.11	$245.10	$245.10
Purchase #3	$120.64	8.708%	$131.1453	$131.15	$131.15	$131.10
Purchase #4	$86.60	4.577%	$90.5637	$90.56	$90.55	$90.60
Purchase #5	$168.29	3.360%	$173.9445	$173.94	$173.95	$173.90
Purchase #6	$133.40	4.655%	$139.6098	$139.61	$139.60	$139.60
Purchase #7	$170.74	5.315%	$179.8148	$179.81	$179.80	$179.80
7 purchase totals =	$1,057.93		$1,131.5007	$1,131.50	$1,131.45	$1,131.40