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	$80.56	5.196%	$84.7459	$84.75	$84.75	$84.70
Purchase #2	$121.28	5.147%	$127.5223	$127.52	$127.50	$127.50
Purchase #3	$50.46	9.682%	$55.3455	$55.35	$55.35	$55.30
Purchase #4	$212.33	3.367%	$219.4792	$219.48	$219.50	$219.50
Purchase #5	$200.42	12.528%	$225.5286	$225.53	$225.55	$225.50
Purchase #6	$6.73	5.715%	$7.1146	$7.11	$7.10	$7.10
Purchase #7	$144.72	7.473%	$155.5349	$155.53	$155.55	$155.50
7 purchase totals =	$816.50		$875.2710	$875.27	$875.30	$875.10