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	$120.28	8.776%	$130.8358	$130.84	$130.85	$130.80
Purchase #2	$87.75	13.825%	$99.8814	$99.88	$99.90	$99.90
Purchase #3	$184.66	11.439%	$205.7833	$205.78	$205.80	$205.80
Purchase #4	$182.71	6.333%	$194.281	$194.28	$194.30	$194.30
Purchase #5	$245.83	8.412%	$266.5092	$266.51	$266.50	$266.50
Purchase #6	$38.29	7.111%	$41.0128	$41.01	$41.00	$41.00
Purchase #7	$78.36	4.625%	$81.9842	$81.98	$82.00	$82.00
7 purchase totals =	$937.88		$1,020.2877	$1,020.28	$1,020.35	$1,020.30