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	$122.53	3.672%	$127.0293	$127.03	$127.05	$127.00
Purchase #2	$179.59	11.804%	$200.7888	$200.79	$200.80	$200.80
Purchase #3	$78.61	9.319%	$85.9357	$85.94	$85.95	$85.90
Purchase #4	$62.82	13.511%	$71.3076	$71.31	$71.30	$71.30
Purchase #5	$86.27	4.380%	$90.0486	$90.05	$90.05	$90.00
Purchase #6	$195.34	10.634%	$216.1125	$216.11	$216.10	$216.10
Purchase #7	$76.77	12.243%	$86.169	$86.17	$86.15	$86.20
7 purchase totals =	$801.93		$877.3915	$877.40	$877.40	$877.30