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	$70.37	4.180%	$73.3115	$73.31	$73.30	$73.30
Purchase #2	$162.99	10.441%	$180.0078	$180.01	$180.00	$180.00
Purchase #3	$151.74	13.474%	$172.1854	$172.19	$172.20	$172.20
Purchase #4	$79.32	12.498%	$89.2334	$89.23	$89.25	$89.20
Purchase #5	$124.49	13.462%	$141.2488	$141.25	$141.25	$141.20
Purchase #6	$169.43	12.274%	$190.2258	$190.23	$190.25	$190.20
Purchase #7	$122.80	6.614%	$130.922	$130.92	$130.90	$130.90
7 purchase totals =	$881.14		$977.1347	$977.14	$977.15	$977.00