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	$54.73	8.330%	$59.289	$59.29	$59.30	$59.30
Purchase #2	$229.60	5.418%	$242.0397	$242.04	$242.05	$242.00
Purchase #3	$188.42	12.413%	$211.8086	$211.81	$211.80	$211.80
Purchase #4	$61.61	3.734%	$63.9105	$63.91	$63.90	$63.90
Purchase #5	$164.53	4.480%	$171.9009	$171.90	$171.90	$171.90
Purchase #6	$61.55	6.265%	$65.4061	$65.41	$65.40	$65.40
Purchase #7	$126.96	3.398%	$131.2741	$131.27	$131.25	$131.30
7 purchase totals =	$887.40		$945.6289	$945.63	$945.60	$945.60