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	$90.67	9.313%	$99.1141	$99.11	$99.10	$99.10
Purchase #2	$139.36	9.471%	$152.5588	$152.56	$152.55	$152.60
Purchase #3	$67.26	7.315%	$72.1801	$72.18	$72.20	$72.20
Purchase #4	$193.81	7.585%	$208.5105	$208.51	$208.50	$208.50
Purchase #5	$12.80	11.760%	$14.3053	$14.31	$14.30	$14.30
Purchase #6	$51.77	3.563%	$53.6146	$53.61	$53.60	$53.60
Purchase #7	$28.36	11.270%	$31.5562	$31.56	$31.55	$31.60
7 purchase totals =	$584.03		$631.8396	$631.84	$631.80	$631.90