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	$6.72	11.244%	$7.4756	$7.48	$7.50	$7.50
Purchase #2	$205.76	9.517%	$225.3422	$225.34	$225.35	$225.30
Purchase #3	$236.81	6.567%	$252.3613	$252.36	$252.35	$252.40
Purchase #4	$93.43	10.130%	$102.8945	$102.89	$102.90	$102.90
Purchase #5	$162.46	7.454%	$174.5698	$174.57	$174.55	$174.60
Purchase #6	$246.31	13.400%	$279.3155	$279.32	$279.30	$279.30
Purchase #7	$182.78	4.583%	$191.1568	$191.16	$191.15	$191.20
7 purchase totals =	$1,134.27		$1,233.1157	$1,233.12	$1,233.10	$1,233.20