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	$29.36	6.441%	$31.2511	$31.25	$31.25	$31.30
Purchase #2	$189.79	8.305%	$205.5521	$205.55	$205.55	$205.60
Purchase #3	$166.37	10.200%	$183.3397	$183.34	$183.35	$183.30
Purchase #4	$53.59	11.463%	$59.733	$59.73	$59.75	$59.70
Purchase #5	$152.25	5.605%	$160.7836	$160.78	$160.80	$160.80
Purchase #6	$46.49	8.285%	$50.3417	$50.34	$50.35	$50.30
Purchase #7	$82.77	3.235%	$85.4476	$85.45	$85.45	$85.40
7 purchase totals =	$720.62		$776.4488	$776.44	$776.50	$776.40