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	$98.98	7.690%	$106.5916	$106.59	$106.60	$106.60
Purchase #2	$69.75	4.575%	$72.9411	$72.94	$72.95	$72.90
Purchase #3	$218.71	11.304%	$243.433	$243.43	$243.45	$243.40
Purchase #4	$86.37	5.343%	$90.9847	$90.98	$91.00	$91.00
Purchase #5	$23.38	5.703%	$24.7134	$24.71	$24.70	$24.70
Purchase #6	$65.70	10.184%	$72.3909	$72.39	$72.40	$72.40
Purchase #7	$197.83	6.300%	$210.2933	$210.29	$210.30	$210.30
7 purchase totals =	$760.72		$821.3480	$821.33	$821.40	$821.30