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	$38.83	9.607%	$42.5604	$42.56	$42.55	$42.60
Purchase #2	$94.55	7.219%	$101.3756	$101.38	$101.40	$101.40
Purchase #3	$77.43	10.796%	$85.7893	$85.79	$85.80	$85.80
Purchase #4	$73.71	11.209%	$81.9722	$81.97	$81.95	$82.00
Purchase #5	$72.94	13.808%	$83.0116	$83.01	$83.00	$83.00
Purchase #6	$33.46	9.199%	$36.538	$36.54	$36.55	$36.50
Purchase #7	$17.72	11.498%	$19.7574	$19.76	$19.75	$19.80
7 purchase totals =	$408.64		$451.0045	$451.01	$451.00	$451.10