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	$223.91	11.407%	$249.4514	$249.45	$249.45	$249.50
Purchase #2	$96.34	3.818%	$100.0183	$100.02	$100.00	$100.00
Purchase #3	$82.86	11.542%	$92.4237	$92.42	$92.40	$92.40
Purchase #4	$209.61	6.635%	$223.5176	$223.52	$223.50	$223.50
Purchase #5	$18.51	5.166%	$19.4662	$19.47	$19.45	$19.50
Purchase #6	$243.92	10.102%	$268.5608	$268.56	$268.55	$268.60
Purchase #7	$29.42	8.653%	$31.9657	$31.97	$31.95	$32.00
7 purchase totals =	$904.57		$985.4037	$985.41	$985.30	$985.50