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	$93.35	9.872%	$102.5655	$102.57	$102.55	$102.60
Purchase #2	$44.51	12.676%	$50.1521	$50.15	$50.15	$50.20
Purchase #3	$167.31	10.553%	$184.9662	$184.97	$184.95	$185.00
Purchase #4	$136.37	11.585%	$152.1685	$152.17	$152.15	$152.20
Purchase #5	$84.26	7.743%	$90.7843	$90.78	$90.80	$90.80
Purchase #6	$31.41	12.478%	$35.3293	$35.33	$35.35	$35.30
Purchase #7	$29.67	13.103%	$33.5577	$33.56	$33.55	$33.60
7 purchase totals =	$586.88		$649.5236	$649.53	$649.50	$649.70