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	$77.45	13.500%	$87.9058	$87.91	$87.90	$87.90
Purchase #2	$173.72	9.844%	$190.821	$190.82	$190.80	$190.80
Purchase #3	$13.44	3.410%	$13.8983	$13.90	$13.90	$13.90
Purchase #4	$136.27	6.623%	$145.2952	$145.30	$145.30	$145.30
Purchase #5	$94.41	7.464%	$101.4568	$101.46	$101.45	$101.50
Purchase #6	$193.43	10.254%	$213.2643	$213.26	$213.25	$213.30
Purchase #7	$207.58	7.292%	$222.7167	$222.72	$222.70	$222.70
7 purchase totals =	$896.30		$975.3581	$975.37	$975.30	$975.40