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	$231.83	12.394%	$260.563	$260.56	$260.55	$260.60
Purchase #2	$88.55	12.170%	$99.3265	$99.33	$99.35	$99.30
Purchase #3	$159.59	5.730%	$168.7345	$168.73	$168.75	$168.70
Purchase #4	$88.29	13.205%	$99.9487	$99.95	$99.95	$99.90
Purchase #5	$27.46	3.650%	$28.4623	$28.46	$28.45	$28.50
Purchase #6	$32.33	11.286%	$35.9788	$35.98	$36.00	$36.00
Purchase #7	$156.70	4.616%	$163.9333	$163.93	$163.95	$163.90
7 purchase totals =	$784.75		$856.9471	$856.94	$857.00	$856.90