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	$202.34	13.434%	$229.5224	$229.52	$229.50	$229.50
Purchase #2	$92.44	6.352%	$98.3118	$98.31	$98.30	$98.30
Purchase #3	$163.91	13.172%	$185.5002	$185.50	$185.50	$185.50
Purchase #4	$106.35	3.706%	$110.2913	$110.29	$110.30	$110.30
Purchase #5	$83.51	6.805%	$89.1929	$89.19	$89.20	$89.20
Purchase #6	$173.53	12.473%	$195.1744	$195.17	$195.15	$195.20
Purchase #7	$247.74	6.514%	$263.8778	$263.88	$263.90	$263.90
7 purchase totals =	$1,069.82		$1,171.8708	$1,171.86	$1,171.85	$1,171.90