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	$98.64	3.289%	$101.8843	$101.88	$101.90	$101.90
Purchase #2	$32.48	7.802%	$35.0141	$35.01	$35.00	$35.00
Purchase #3	$172.88	10.337%	$190.7506	$190.75	$190.75	$190.80
Purchase #4	$182.64	7.535%	$196.4019	$196.40	$196.40	$196.40
Purchase #5	$146.50	10.857%	$162.4055	$162.41	$162.40	$162.40
Purchase #6	$245.78	4.508%	$256.8598	$256.86	$256.85	$256.90
Purchase #7	$27.59	8.184%	$29.848	$29.85	$29.85	$29.80
7 purchase totals =	$906.51		$973.1642	$973.16	$973.15	$973.20