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	$216.55	4.793%	$226.9292	$226.93	$226.95	$226.90
Purchase #2	$79.60	7.785%	$85.7969	$85.80	$85.80	$85.80
Purchase #3	$57.82	6.334%	$61.4823	$61.48	$61.50	$61.50
Purchase #4	$55.74	3.329%	$57.5956	$57.60	$57.60	$57.60
Purchase #5	$8.33	13.585%	$9.4616	$9.46	$9.45	$9.50
Purchase #6	$67.71	6.640%	$72.2059	$72.21	$72.20	$72.20
Purchase #7	$43.55	5.115%	$45.7776	$45.78	$45.80	$45.80
7 purchase totals =	$529.30		$559.2491	$559.26	$559.30	$559.30