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	$143.26	8.309%	$155.1635	$155.16	$155.15	$155.20
Purchase #2	$87.39	12.798%	$98.5742	$98.57	$98.55	$98.60
Purchase #3	$31.48	12.457%	$35.4015	$35.40	$35.40	$35.40
Purchase #4	$209.37	7.695%	$225.481	$225.48	$225.50	$225.50
Purchase #5	$139.28	11.585%	$155.4156	$155.42	$155.40	$155.40
Purchase #6	$85.40	5.399%	$90.0107	$90.01	$90.00	$90.00
Purchase #7	$5.85	5.770%	$6.1875	$6.19	$6.20	$6.20
7 purchase totals =	$702.03		$766.2340	$766.23	$766.20	$766.30