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	$39.89	5.769%	$42.1913	$42.19	$42.20	$42.20
Purchase #2	$139.88	11.828%	$156.425	$156.43	$156.45	$156.40
Purchase #3	$111.86	7.801%	$120.5862	$120.59	$120.60	$120.60
Purchase #4	$88.99	3.570%	$92.1669	$92.17	$92.15	$92.20
Purchase #5	$95.26	6.346%	$101.3052	$101.31	$101.30	$101.30
Purchase #6	$85.41	6.261%	$90.7575	$90.76	$90.75	$90.80
Purchase #7	$192.60	8.339%	$208.6609	$208.66	$208.65	$208.70
7 purchase totals =	$753.89		$812.0930	$812.11	$812.10	$812.20