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	$5.57	6.753%	$5.9461	$5.95	$5.95	$5.90
Purchase #2	$72.38	6.408%	$77.0181	$77.02	$77.00	$77.00
Purchase #3	$24.41	10.662%	$27.0126	$27.01	$27.00	$27.00
Purchase #4	$238.52	10.811%	$264.3064	$264.31	$264.30	$264.30
Purchase #5	$221.30	9.541%	$242.4142	$242.41	$242.40	$242.40
Purchase #6	$19.89	8.185%	$21.518	$21.52	$21.50	$21.50
Purchase #7	$98.39	11.672%	$109.8741	$109.87	$109.85	$109.90
7 purchase totals =	$680.46		$748.0895	$748.09	$748.00	$748.00