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	$140.64	12.546%	$158.2847	$158.28	$158.30	$158.30
Purchase #2	$72.59	11.450%	$80.9016	$80.90	$80.90	$80.90
Purchase #3	$245.92	9.492%	$269.2627	$269.26	$269.25	$269.30
Purchase #4	$74.91	11.126%	$83.2445	$83.24	$83.25	$83.20
Purchase #5	$191.30	9.785%	$210.0187	$210.02	$210.00	$210.00
Purchase #6	$182.36	7.871%	$196.7136	$196.71	$196.70	$196.70
Purchase #7	$91.76	10.570%	$101.459	$101.46	$101.45	$101.50
7 purchase totals =	$999.48		$1,099.8848	$1,099.87	$1,099.85	$1,099.90