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	$74.56	4.661%	$78.0352	$78.04	$78.05	$78.00
Purchase #2	$42.75	7.275%	$45.8601	$45.86	$45.85	$45.90
Purchase #3	$234.32	6.351%	$249.2017	$249.20	$249.20	$249.20
Purchase #4	$85.90	4.594%	$89.8462	$89.85	$89.85	$89.80
Purchase #5	$98.82	12.765%	$111.4344	$111.43	$111.45	$111.40
Purchase #6	$83.66	5.787%	$88.5014	$88.50	$88.50	$88.50
Purchase #7	$142.69	10.469%	$157.6282	$157.63	$157.65	$157.60
7 purchase totals =	$762.70		$820.5072	$820.51	$820.55	$820.40