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	$78.72	3.633%	$81.5799	$81.58	$81.60	$81.60
Purchase #2	$240.43	10.459%	$265.5766	$265.58	$265.60	$265.60
Purchase #3	$123.76	3.395%	$127.9617	$127.96	$127.95	$128.00
Purchase #4	$88.82	6.709%	$94.7789	$94.78	$94.80	$94.80
Purchase #5	$98.94	6.358%	$105.2306	$105.23	$105.25	$105.20
Purchase #6	$70.73	5.812%	$74.8408	$74.84	$74.85	$74.80
Purchase #7	$175.57	9.272%	$191.8489	$191.85	$191.85	$191.80
7 purchase totals =	$876.97		$941.8174	$941.82	$941.90	$941.80