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	$92.32	8.609%	$100.2678	$100.27	$100.25	$100.30
Purchase #2	$175.54	10.837%	$194.5633	$194.56	$194.55	$194.60
Purchase #3	$131.52	11.709%	$146.9197	$146.92	$146.90	$146.90
Purchase #4	$104.48	6.527%	$111.2994	$111.30	$111.30	$111.30
Purchase #5	$49.49	12.796%	$55.8227	$55.82	$55.80	$55.80
Purchase #6	$209.30	5.483%	$220.7759	$220.78	$220.80	$220.80
Purchase #7	$168.37	12.542%	$189.487	$189.49	$189.50	$189.50
7 purchase totals =	$931.02		$1,019.1358	$1,019.14	$1,019.10	$1,019.20