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	$6.90	8.813%	$7.5081	$7.51	$7.50	$7.50
Purchase #2	$139.59	13.756%	$158.792	$158.79	$158.80	$158.80
Purchase #3	$82.27	13.550%	$93.4176	$93.42	$93.40	$93.40
Purchase #4	$192.79	3.484%	$199.5068	$199.51	$199.50	$199.50
Purchase #5	$128.50	9.345%	$140.5083	$140.51	$140.50	$140.50
Purchase #6	$91.94	11.283%	$102.3136	$102.31	$102.30	$102.30
Purchase #7	$200.38	6.141%	$212.6853	$212.69	$212.70	$212.70
7 purchase totals =	$842.37		$914.7317	$914.74	$914.70	$914.70