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	$170.48	8.564%	$185.0799	$185.08	$185.10	$185.10
Purchase #2	$101.59	7.593%	$109.3037	$109.30	$109.30	$109.30
Purchase #3	$79.95	13.680%	$90.8872	$90.89	$90.90	$90.90
Purchase #4	$241.35	3.715%	$250.3162	$250.32	$250.30	$250.30
Purchase #5	$5.98	4.452%	$6.2462	$6.25	$6.25	$6.20
Purchase #6	$81.77	10.428%	$90.297	$90.30	$90.30	$90.30
Purchase #7	$241.66	13.658%	$274.6659	$274.67	$274.65	$274.70
7 purchase totals =	$922.78		$1,006.7961	$1,006.81	$1,006.80	$1,006.80