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	$120.50	6.673%	$128.541	$128.54	$128.55	$128.50
Purchase #2	$33.64	12.841%	$37.9597	$37.96	$37.95	$38.00
Purchase #3	$15.66	8.118%	$16.9313	$16.93	$16.95	$16.90
Purchase #4	$142.51	3.704%	$147.7886	$147.79	$147.80	$147.80
Purchase #5	$83.33	8.338%	$90.2781	$90.28	$90.30	$90.30
Purchase #6	$201.37	3.562%	$208.5428	$208.54	$208.55	$208.50
Purchase #7	$39.45	3.409%	$40.7949	$40.79	$40.80	$40.80
7 purchase totals =	$636.46		$670.8364	$670.83	$670.90	$670.80