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	$156.59	7.835%	$168.8588	$168.86	$168.85	$168.90
Purchase #2	$250.32	9.477%	$274.0428	$274.04	$274.05	$274.00
Purchase #3	$72.89	9.542%	$79.8452	$79.85	$79.85	$79.80
Purchase #4	$229.97	9.355%	$251.4837	$251.48	$251.50	$251.50
Purchase #5	$234.37	3.278%	$242.0526	$242.05	$242.05	$242.10
Purchase #6	$54.38	10.239%	$59.948	$59.95	$59.95	$59.90
Purchase #7	$84.52	6.488%	$90.0037	$90.00	$90.00	$90.00
7 purchase totals =	$1,083.04		$1,166.2348	$1,166.23	$1,166.25	$1,166.20