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	$157.58	6.223%	$167.3862	$167.39	$167.40	$167.40
Purchase #2	$158.29	4.165%	$164.8828	$164.88	$164.90	$164.90
Purchase #3	$57.36	11.486%	$63.9484	$63.95	$63.95	$63.90
Purchase #4	$31.67	6.841%	$33.8365	$33.84	$33.85	$33.80
Purchase #5	$86.57	3.722%	$89.7921	$89.79	$89.80	$89.80
Purchase #6	$33.72	6.351%	$35.8616	$35.86	$35.85	$35.90
Purchase #7	$119.58	9.516%	$130.9592	$130.96	$130.95	$131.00
7 purchase totals =	$644.77		$686.6668	$686.67	$686.70	$686.70