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	$131.39	7.800%	$141.6384	$141.64	$141.65	$141.60
Purchase #2	$25.76	10.294%	$28.4117	$28.41	$28.40	$28.40
Purchase #3	$95.53	8.219%	$103.3816	$103.38	$103.40	$103.40
Purchase #4	$198.80	13.141%	$224.9243	$224.92	$224.90	$224.90
Purchase #5	$183.32	3.424%	$189.5969	$189.60	$189.60	$189.60
Purchase #6	$212.75	11.151%	$236.4738	$236.47	$236.45	$236.50
Purchase #7	$247.39	7.191%	$265.1798	$265.18	$265.20	$265.20
7 purchase totals =	$1,094.94		$1,189.6065	$1,189.60	$1,189.60	$1,189.60