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	$101.67	3.691%	$105.4226	$105.42	$105.40	$105.40
Purchase #2	$24.72	13.409%	$28.0347	$28.03	$28.05	$28.00
Purchase #3	$104.47	5.553%	$110.2712	$110.27	$110.25	$110.30
Purchase #4	$180.91	9.588%	$198.2557	$198.26	$198.25	$198.30
Purchase #5	$246.99	11.494%	$275.379	$275.38	$275.40	$275.40
Purchase #6	$72.45	8.291%	$78.4568	$78.46	$78.45	$78.50
Purchase #7	$116.33	13.397%	$131.9147	$131.91	$131.90	$131.90
7 purchase totals =	$847.54		$927.7347	$927.73	$927.70	$927.80