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	$66.84	9.681%	$73.3108	$73.31	$73.30	$73.30
Purchase #2	$205.52	12.660%	$231.5388	$231.54	$231.55	$231.50
Purchase #3	$67.91	6.768%	$72.5061	$72.51	$72.50	$72.50
Purchase #4	$155.61	9.279%	$170.0491	$170.05	$170.05	$170.00
Purchase #5	$138.31	12.332%	$155.3664	$155.37	$155.35	$155.40
Purchase #6	$169.49	9.622%	$185.7983	$185.80	$185.80	$185.80
Purchase #7	$159.77	12.146%	$179.1757	$179.18	$179.20	$179.20
7 purchase totals =	$963.45		$1,067.7452	$1,067.76	$1,067.75	$1,067.70