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	$8.36	6.295%	$8.8863	$8.89	$8.90	$8.90
Purchase #2	$80.45	5.850%	$85.1563	$85.16	$85.15	$85.20
Purchase #3	$146.31	12.530%	$164.6426	$164.64	$164.65	$164.60
Purchase #4	$57.50	9.807%	$63.139	$63.14	$63.15	$63.10
Purchase #5	$112.70	4.115%	$117.3376	$117.34	$117.35	$117.30
Purchase #6	$59.84	8.446%	$64.8941	$64.89	$64.90	$64.90
Purchase #7	$30.38	12.503%	$34.1784	$34.18	$34.20	$34.20
7 purchase totals =	$495.54		$538.2343	$538.24	$538.30	$538.20