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	$9.88	6.109%	$10.4836	$10.48	$10.50	$10.50
Purchase #2	$206.39	4.816%	$216.3297	$216.33	$216.35	$216.30
Purchase #3	$57.80	6.478%	$61.5443	$61.54	$61.55	$61.50
Purchase #4	$219.68	10.288%	$242.2807	$242.28	$242.30	$242.30
Purchase #5	$191.87	7.544%	$206.3447	$206.34	$206.35	$206.30
Purchase #6	$169.90	7.342%	$182.3741	$182.37	$182.35	$182.40
Purchase #7	$56.48	4.420%	$58.9764	$58.98	$59.00	$59.00
7 purchase totals =	$912.00		$978.3335	$978.32	$978.40	$978.30