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	$115.35	9.319%	$126.0995	$126.10	$126.10	$126.10
Purchase #2	$41.82	3.459%	$43.2666	$43.27	$43.25	$43.30
Purchase #3	$160.53	6.871%	$171.56	$171.56	$171.55	$171.60
Purchase #4	$40.90	3.362%	$42.2751	$42.28	$42.30	$42.30
Purchase #5	$137.80	10.856%	$152.7596	$152.76	$152.75	$152.80
Purchase #6	$84.60	6.206%	$89.8503	$89.85	$89.85	$89.90
Purchase #7	$205.77	11.709%	$229.8636	$229.86	$229.85	$229.90
7 purchase totals =	$786.77		$855.6747	$855.68	$855.65	$855.90