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	$109.78	12.302%	$123.2851	$123.29	$123.30	$123.30
Purchase #2	$171.96	4.115%	$179.0362	$179.04	$179.05	$179.00
Purchase #3	$62.96	10.191%	$69.3763	$69.38	$69.40	$69.40
Purchase #4	$85.86	3.689%	$89.0274	$89.03	$89.05	$89.00
Purchase #5	$210.40	8.523%	$228.3324	$228.33	$228.35	$228.30
Purchase #6	$45.79	8.618%	$49.7362	$49.74	$49.75	$49.70
Purchase #7	$166.68	10.321%	$183.883	$183.88	$183.90	$183.90
7 purchase totals =	$853.43		$922.6766	$922.69	$922.80	$922.60