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	$89.66	12.712%	$101.0576	$101.06	$101.05	$101.10
Purchase #2	$154.83	8.463%	$167.9333	$167.93	$167.95	$167.90
Purchase #3	$52.55	12.857%	$59.3064	$59.31	$59.30	$59.30
Purchase #4	$216.68	10.774%	$240.0251	$240.03	$240.05	$240.00
Purchase #5	$198.42	13.329%	$224.8674	$224.87	$224.85	$224.90
Purchase #6	$72.48	7.559%	$77.9588	$77.96	$77.95	$78.00
Purchase #7	$5.36	9.716%	$5.8808	$5.88	$5.90	$5.90
7 purchase totals =	$789.98		$877.0294	$877.04	$877.05	$877.10