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	$246.90	7.817%	$266.2002	$266.20	$266.20	$266.20
Purchase #2	$88.61	12.417%	$99.6127	$99.61	$99.60	$99.60
Purchase #3	$52.55	12.241%	$58.9826	$58.98	$59.00	$59.00
Purchase #4	$104.71	11.117%	$116.3506	$116.35	$116.35	$116.40
Purchase #5	$209.44	5.774%	$221.5331	$221.53	$221.55	$221.50
Purchase #6	$142.73	7.222%	$153.038	$153.04	$153.05	$153.00
Purchase #7	$138.94	8.335%	$150.5206	$150.52	$150.50	$150.50
7 purchase totals =	$983.88		$1,066.2378	$1,066.23	$1,066.25	$1,066.20