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	$134.79	3.556%	$139.5831	$139.58	$139.60	$139.60
Purchase #2	$90.35	8.850%	$98.346	$98.35	$98.35	$98.30
Purchase #3	$132.73	13.199%	$150.249	$150.25	$150.25	$150.20
Purchase #4	$81.60	9.651%	$89.4752	$89.48	$89.50	$89.50
Purchase #5	$39.52	9.332%	$43.208	$43.21	$43.20	$43.20
Purchase #6	$188.88	8.256%	$204.4739	$204.47	$204.45	$204.50
Purchase #7	$119.74	4.299%	$124.8876	$124.89	$124.90	$124.90
7 purchase totals =	$787.61		$850.2228	$850.23	$850.25	$850.20