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	$155.33	8.729%	$168.8888	$168.89	$168.90	$168.90
Purchase #2	$198.30	8.333%	$214.8243	$214.82	$214.80	$214.80
Purchase #3	$222.56	7.360%	$238.9404	$238.94	$238.95	$238.90
Purchase #4	$22.59	12.545%	$25.4239	$25.42	$25.40	$25.40
Purchase #5	$71.58	12.510%	$80.5347	$80.53	$80.55	$80.50
Purchase #6	$195.60	12.731%	$220.5018	$220.50	$220.50	$220.50
Purchase #7	$44.69	5.482%	$47.1399	$47.14	$47.15	$47.10
7 purchase totals =	$910.65		$996.2538	$996.24	$996.25	$996.10