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	$125.98	9.141%	$137.4958	$137.50	$137.50	$137.50
Purchase #2	$109.35	10.251%	$120.5595	$120.56	$120.55	$120.60
Purchase #3	$40.27	6.321%	$42.8155	$42.82	$42.80	$42.80
Purchase #4	$89.55	8.199%	$96.8922	$96.89	$96.90	$96.90
Purchase #5	$179.65	6.523%	$191.3686	$191.37	$191.35	$191.40
Purchase #6	$179.39	11.758%	$200.4827	$200.48	$200.50	$200.50
Purchase #7	$58.66	8.561%	$63.6819	$63.68	$63.70	$63.70
7 purchase totals =	$782.85		$853.2962	$853.30	$853.30	$853.40