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	$164.44	11.618%	$183.5446	$183.54	$183.55	$183.50
Purchase #2	$61.92	9.180%	$67.6043	$67.60	$67.60	$67.60
Purchase #3	$142.88	8.713%	$155.3291	$155.33	$155.35	$155.30
Purchase #4	$131.67	4.452%	$137.5319	$137.53	$137.55	$137.50
Purchase #5	$136.64	3.343%	$141.2079	$141.21	$141.20	$141.20
Purchase #6	$89.81	11.287%	$99.9469	$99.95	$99.95	$99.90
Purchase #7	$47.72	5.393%	$50.2935	$50.29	$50.30	$50.30
7 purchase totals =	$775.08		$835.4582	$835.45	$835.50	$835.30