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	$138.34	13.790%	$157.4171	$157.42	$157.40	$157.40
Purchase #2	$91.43	8.446%	$99.1522	$99.15	$99.15	$99.20
Purchase #3	$141.68	10.465%	$156.5068	$156.51	$156.50	$156.50
Purchase #4	$43.41	8.834%	$47.2448	$47.24	$47.25	$47.20
Purchase #5	$230.79	9.570%	$252.8766	$252.88	$252.90	$252.90
Purchase #6	$65.29	11.529%	$72.8173	$72.82	$72.80	$72.80
Purchase #7	$131.56	4.547%	$137.542	$137.54	$137.55	$137.50
7 purchase totals =	$842.50		$923.5568	$923.56	$923.55	$923.50