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	$75.85	3.434%	$78.4547	$78.45	$78.45	$78.50
Purchase #2	$56.70	11.581%	$63.2664	$63.27	$63.25	$63.30
Purchase #3	$21.37	6.576%	$22.7753	$22.78	$22.80	$22.80
Purchase #4	$33.31	12.166%	$37.3625	$37.36	$37.35	$37.40
Purchase #5	$31.33	3.457%	$32.4131	$32.41	$32.40	$32.40
Purchase #6	$144.80	3.775%	$150.2662	$150.27	$150.25	$150.30
Purchase #7	$27.69	9.223%	$30.2438	$30.24	$30.25	$30.20
7 purchase totals =	$391.05		$414.7820	$414.78	$414.75	$414.90