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	$130.89	12.179%	$146.8311	$146.83	$146.85	$146.80
Purchase #2	$215.92	3.695%	$223.8982	$223.90	$223.90	$223.90
Purchase #3	$38.41	13.171%	$43.469	$43.47	$43.45	$43.50
Purchase #4	$93.56	5.572%	$98.7732	$98.77	$98.75	$98.80
Purchase #5	$85.78	3.839%	$89.0731	$89.07	$89.05	$89.10
Purchase #6	$73.76	11.567%	$82.2918	$82.29	$82.30	$82.30
Purchase #7	$64.72	8.816%	$70.4257	$70.43	$70.45	$70.40
7 purchase totals =	$703.04		$754.7621	$754.76	$754.75	$754.80