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	$131.57	7.486%	$141.4193	$141.42	$141.40	$141.40
Purchase #2	$131.61	3.539%	$136.2677	$136.27	$136.25	$136.30
Purchase #3	$218.46	3.606%	$226.3377	$226.34	$226.35	$226.30
Purchase #4	$98.44	13.128%	$111.3632	$111.36	$111.35	$111.40
Purchase #5	$239.34	11.575%	$267.0436	$267.04	$267.05	$267.00
Purchase #6	$16.35	11.836%	$18.2852	$18.29	$18.30	$18.30
Purchase #7	$38.50	9.480%	$42.1498	$42.15	$42.15	$42.10
7 purchase totals =	$874.27		$942.8665	$942.87	$942.85	$942.80