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	$138.54	6.776%	$147.9275	$147.93	$147.95	$147.90
Purchase #2	$43.44	5.742%	$45.9343	$45.93	$45.95	$45.90
Purchase #3	$94.79	9.292%	$103.5979	$103.60	$103.60	$103.60
Purchase #4	$242.61	10.759%	$268.7124	$268.71	$268.70	$268.70
Purchase #5	$151.58	13.799%	$172.4965	$172.50	$172.50	$172.50
Purchase #6	$209.90	3.807%	$217.8909	$217.89	$217.90	$217.90
Purchase #7	$246.35	10.520%	$272.266	$272.27	$272.25	$272.30
7 purchase totals =	$1,127.21		$1,228.8255	$1,228.83	$1,228.85	$1,228.80