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	$157.28	4.420%	$164.2318	$164.23	$164.25	$164.20
Purchase #2	$213.96	9.313%	$233.8861	$233.89	$233.90	$233.90
Purchase #3	$57.70	4.414%	$60.2469	$60.25	$60.25	$60.20
Purchase #4	$89.33	9.112%	$97.4697	$97.47	$97.45	$97.50
Purchase #5	$19.98	3.668%	$20.7129	$20.71	$20.70	$20.70
Purchase #6	$173.31	5.327%	$182.5422	$182.54	$182.55	$182.50
Purchase #7	$125.69	4.631%	$131.5107	$131.51	$131.50	$131.50
7 purchase totals =	$837.25		$890.6003	$890.60	$890.60	$890.50