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	$89.89	11.655%	$100.3667	$100.37	$100.35	$100.40
Purchase #2	$136.89	4.273%	$142.7393	$142.74	$142.75	$142.70
Purchase #3	$225.78	8.515%	$245.0052	$245.01	$245.00	$245.00
Purchase #4	$18.56	13.560%	$21.0767	$21.08	$21.10	$21.10
Purchase #5	$232.99	10.839%	$258.2438	$258.24	$258.25	$258.20
Purchase #6	$135.27	7.792%	$145.8102	$145.81	$145.80	$145.80
Purchase #7	$9.56	7.862%	$10.3116	$10.31	$10.30	$10.30
7 purchase totals =	$848.94		$923.5535	$923.56	$923.55	$923.50