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	$45.57	4.747%	$47.7332	$47.73	$47.75	$47.70
Purchase #2	$56.84	4.208%	$59.2318	$59.23	$59.25	$59.20
Purchase #3	$224.33	7.110%	$240.2799	$240.28	$240.30	$240.30
Purchase #4	$161.70	9.393%	$176.8885	$176.89	$176.90	$176.90
Purchase #5	$156.48	9.586%	$171.4802	$171.48	$171.50	$171.50
Purchase #6	$41.43	12.337%	$46.5412	$46.54	$46.55	$46.50
Purchase #7	$114.70	11.186%	$127.5303	$127.53	$127.55	$127.50
7 purchase totals =	$801.05		$869.6851	$869.68	$869.80	$869.60