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	$77.57	8.135%	$83.8803	$83.88	$83.90	$83.90
Purchase #2	$145.62	13.391%	$165.12	$165.12	$165.10	$165.10
Purchase #3	$152.72	8.435%	$165.6019	$165.60	$165.60	$165.60
Purchase #4	$184.84	13.582%	$209.945	$209.95	$209.95	$209.90
Purchase #5	$82.45	12.383%	$92.6598	$92.66	$92.65	$92.70
Purchase #6	$187.96	4.466%	$196.3543	$196.35	$196.35	$196.40
Purchase #7	$86.86	3.652%	$90.0321	$90.03	$90.05	$90.00
7 purchase totals =	$918.02		$1,003.5934	$1,003.59	$1,003.60	$1,003.60