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	$98.52	9.781%	$108.1562	$108.16	$108.15	$108.20
Purchase #2	$36.54	3.432%	$37.7941	$37.79	$37.80	$37.80
Purchase #3	$151.61	8.580%	$164.6181	$164.62	$164.60	$164.60
Purchase #4	$171.59	11.565%	$191.4344	$191.43	$191.45	$191.40
Purchase #5	$211.67	9.381%	$231.5268	$231.53	$231.55	$231.50
Purchase #6	$246.68	7.638%	$265.5214	$265.52	$265.50	$265.50
Purchase #7	$73.73	13.740%	$83.8605	$83.86	$83.85	$83.90
7 purchase totals =	$990.34		$1,082.9115	$1,082.91	$1,082.90	$1,082.90