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	$129.89	12.750%	$146.451	$146.45	$146.45	$146.50
Purchase #2	$123.88	7.799%	$133.5414	$133.54	$133.55	$133.50
Purchase #3	$135.55	10.844%	$150.249	$150.25	$150.25	$150.20
Purchase #4	$180.72	5.442%	$190.5548	$190.55	$190.55	$190.60
Purchase #5	$179.78	3.299%	$185.7109	$185.71	$185.70	$185.70
Purchase #6	$160.50	11.277%	$178.5996	$178.60	$178.60	$178.60
Purchase #7	$216.33	12.770%	$243.9553	$243.96	$243.95	$244.00
7 purchase totals =	$1,126.65		$1,229.0620	$1,229.06	$1,229.05	$1,229.10