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	$150.25	6.169%	$159.5189	$159.52	$159.50	$159.50
Purchase #2	$80.58	13.510%	$91.4664	$91.47	$91.45	$91.50
Purchase #3	$248.44	5.421%	$261.9079	$261.91	$261.90	$261.90
Purchase #4	$59.79	12.130%	$67.0425	$67.04	$67.05	$67.00
Purchase #5	$145.67	10.814%	$161.4228	$161.42	$161.40	$161.40
Purchase #6	$232.98	13.803%	$265.1382	$265.14	$265.15	$265.10
Purchase #7	$12.60	9.755%	$13.8291	$13.83	$13.85	$13.80
7 purchase totals =	$930.31		$1,020.3258	$1,020.33	$1,020.30	$1,020.20