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	$135.73	11.162%	$150.8802	$150.88	$150.90	$150.90
Purchase #2	$67.91	3.264%	$70.1266	$70.13	$70.15	$70.10
Purchase #3	$130.38	12.445%	$146.6058	$146.61	$146.60	$146.60
Purchase #4	$114.61	5.789%	$121.2448	$121.24	$121.25	$121.20
Purchase #5	$249.90	5.433%	$263.4771	$263.48	$263.50	$263.50
Purchase #6	$130.90	6.457%	$139.3522	$139.35	$139.35	$139.40
Purchase #7	$155.72	6.444%	$165.7546	$165.75	$165.75	$165.80
7 purchase totals =	$985.15		$1,057.4413	$1,057.44	$1,057.50	$1,057.50