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	$83.45	7.359%	$89.5911	$89.59	$89.60	$89.60
Purchase #2	$183.31	11.197%	$203.8352	$203.84	$203.85	$203.80
Purchase #3	$74.30	8.343%	$80.4988	$80.50	$80.50	$80.50
Purchase #4	$232.94	13.746%	$264.9599	$264.96	$264.95	$265.00
Purchase #5	$143.25	5.731%	$151.4597	$151.46	$151.45	$151.50
Purchase #6	$213.90	7.616%	$230.1906	$230.19	$230.20	$230.20
Purchase #7	$196.89	7.851%	$212.3478	$212.35	$212.35	$212.30
7 purchase totals =	$1,128.04		$1,232.8831	$1,232.89	$1,232.90	$1,232.90