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	$125.78	10.851%	$139.4284	$139.43	$139.45	$139.40
Purchase #2	$81.28	11.108%	$90.3086	$90.31	$90.30	$90.30
Purchase #3	$202.67	3.672%	$210.112	$210.11	$210.10	$210.10
Purchase #4	$110.97	7.392%	$119.1729	$119.17	$119.15	$119.20
Purchase #5	$82.62	11.859%	$92.4179	$92.42	$92.40	$92.40
Purchase #6	$81.29	5.728%	$85.9463	$85.95	$85.95	$85.90
Purchase #7	$12.74	13.800%	$14.4981	$14.50	$14.50	$14.50
7 purchase totals =	$697.35		$751.8842	$751.89	$751.85	$751.80