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	$230.47	10.655%	$255.0266	$255.03	$255.05	$255.00
Purchase #2	$124.59	10.224%	$137.3281	$137.33	$137.35	$137.30
Purchase #3	$228.89	13.546%	$259.8954	$259.90	$259.90	$259.90
Purchase #4	$141.74	9.362%	$155.0097	$155.01	$155.00	$155.00
Purchase #5	$76.78	9.285%	$83.909	$83.91	$83.90	$83.90
Purchase #6	$120.89	7.396%	$129.831	$129.83	$129.85	$129.80
Purchase #7	$125.96	9.370%	$137.7625	$137.76	$137.75	$137.80
7 purchase totals =	$1,049.32		$1,158.7623	$1,158.77	$1,158.80	$1,158.70