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	$101.85	6.785%	$108.7605	$108.76	$108.75	$108.80
Purchase #2	$172.73	10.494%	$190.8563	$190.86	$190.85	$190.90
Purchase #3	$150.71	4.234%	$157.0911	$157.09	$157.10	$157.10
Purchase #4	$152.43	12.855%	$172.0249	$172.02	$172.00	$172.00
Purchase #5	$38.59	10.478%	$42.6335	$42.63	$42.65	$42.60
Purchase #6	$156.43	7.702%	$168.4782	$168.48	$168.50	$168.50
Purchase #7	$119.77	7.799%	$129.1109	$129.11	$129.10	$129.10
7 purchase totals =	$892.51		$968.9554	$968.95	$968.95	$969.00