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	$51.37	13.119%	$58.1092	$58.11	$58.10	$58.10
Purchase #2	$185.51	10.685%	$205.3317	$205.33	$205.35	$205.30
Purchase #3	$110.98	11.187%	$123.3953	$123.40	$123.40	$123.40
Purchase #4	$103.99	7.349%	$111.6322	$111.63	$111.65	$111.60
Purchase #5	$93.88	8.503%	$101.8626	$101.86	$101.85	$101.90
Purchase #6	$149.37	10.296%	$164.7491	$164.75	$164.75	$164.70
Purchase #7	$83.51	10.762%	$92.4973	$92.50	$92.50	$92.50
7 purchase totals =	$778.61		$857.5774	$857.58	$857.60	$857.50