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	$47.37	6.630%	$50.5106	$50.51	$50.50	$50.50
Purchase #2	$29.56	4.121%	$30.7782	$30.78	$30.80	$30.80
Purchase #3	$90.86	3.872%	$94.3781	$94.38	$94.40	$94.40
Purchase #4	$204.77	11.683%	$228.6933	$228.69	$228.70	$228.70
Purchase #5	$119.36	10.218%	$131.5562	$131.56	$131.55	$131.60
Purchase #6	$151.31	9.675%	$165.9492	$165.95	$165.95	$165.90
Purchase #7	$142.35	13.364%	$161.3737	$161.37	$161.35	$161.40
7 purchase totals =	$785.58		$863.2393	$863.24	$863.25	$863.30