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	$82.36	8.741%	$89.5591	$89.56	$89.55	$89.60
Purchase #2	$210.38	10.700%	$232.8907	$232.89	$232.90	$232.90
Purchase #3	$25.30	10.690%	$28.0046	$28.00	$28.00	$28.00
Purchase #4	$41.68	4.683%	$43.6319	$43.63	$43.65	$43.60
Purchase #5	$144.66	9.761%	$158.7803	$158.78	$158.80	$158.80
Purchase #6	$149.49	12.353%	$167.9565	$167.96	$167.95	$168.00
Purchase #7	$135.44	12.689%	$152.626	$152.63	$152.65	$152.60
7 purchase totals =	$789.31		$873.4491	$873.45	$873.50	$873.50