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	$48.44	13.115%	$54.7929	$54.79	$54.80	$54.80
Purchase #2	$135.88	12.666%	$153.0906	$153.09	$153.10	$153.10
Purchase #3	$162.82	9.665%	$178.5566	$178.56	$178.55	$178.60
Purchase #4	$81.71	5.361%	$86.0905	$86.09	$86.10	$86.10
Purchase #5	$171.93	11.610%	$191.8911	$191.89	$191.90	$191.90
Purchase #6	$74.99	11.134%	$83.3394	$83.34	$83.35	$83.30
Purchase #7	$98.82	4.347%	$103.1157	$103.12	$103.10	$103.10
7 purchase totals =	$774.59		$850.8768	$850.88	$850.90	$850.90