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	$233.63	9.282%	$255.3155	$255.32	$255.30	$255.30
Purchase #2	$80.44	10.603%	$88.9691	$88.97	$88.95	$89.00
Purchase #3	$132.75	6.380%	$141.2195	$141.22	$141.20	$141.20
Purchase #4	$78.74	6.455%	$83.8227	$83.82	$83.80	$83.80
Purchase #5	$101.72	7.304%	$109.1496	$109.15	$109.15	$109.10
Purchase #6	$90.71	3.400%	$93.7941	$93.79	$93.80	$93.80
Purchase #7	$170.79	6.866%	$182.5164	$182.52	$182.50	$182.50
7 purchase totals =	$888.78		$954.7869	$954.79	$954.70	$954.70