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	$158.57	4.728%	$166.0672	$166.07	$166.05	$166.10
Purchase #2	$36.57	10.222%	$40.3082	$40.31	$40.30	$40.30
Purchase #3	$20.75	11.498%	$23.1358	$23.14	$23.15	$23.10
Purchase #4	$209.44	4.382%	$218.6177	$218.62	$218.60	$218.60
Purchase #5	$64.48	11.344%	$71.7946	$71.79	$71.80	$71.80
Purchase #6	$95.42	5.564%	$100.7292	$100.73	$100.75	$100.70
Purchase #7	$170.27	7.248%	$182.6112	$182.61	$182.60	$182.60
7 purchase totals =	$755.50		$803.2639	$803.27	$803.25	$803.20