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	$174.99	7.663%	$188.3995	$188.40	$188.40	$188.40
Purchase #2	$164.61	8.645%	$178.8405	$178.84	$178.85	$178.80
Purchase #3	$102.37	9.111%	$111.6969	$111.70	$111.70	$111.70
Purchase #4	$59.29	13.716%	$67.4222	$67.42	$67.40	$67.40
Purchase #5	$185.59	7.482%	$199.4758	$199.48	$199.50	$199.50
Purchase #6	$78.54	5.686%	$83.0058	$83.01	$83.00	$83.00
Purchase #7	$246.57	11.344%	$274.5409	$274.54	$274.55	$274.50
7 purchase totals =	$1,011.96		$1,103.3816	$1,103.39	$1,103.40	$1,103.30