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	$122.78	3.747%	$127.3806	$127.38	$127.40	$127.40
Purchase #2	$52.88	12.361%	$59.4165	$59.42	$59.40	$59.40
Purchase #3	$249.99	9.442%	$273.5941	$273.59	$273.60	$273.60
Purchase #4	$236.49	10.525%	$261.3806	$261.38	$261.40	$261.40
Purchase #5	$209.57	11.461%	$233.5888	$233.59	$233.60	$233.60
Purchase #6	$134.71	3.752%	$139.7643	$139.76	$139.75	$139.80
Purchase #7	$84.86	9.317%	$92.7664	$92.77	$92.75	$92.80
7 purchase totals =	$1,091.28		$1,187.8913	$1,187.89	$1,187.90	$1,188.00