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	$54.98	5.264%	$57.8741	$57.87	$57.85	$57.90
Purchase #2	$34.33	3.136%	$35.4066	$35.41	$35.40	$35.40
Purchase #3	$156.62	9.170%	$170.9821	$170.98	$171.00	$171.00
Purchase #4	$30.95	11.244%	$34.43	$34.43	$34.45	$34.40
Purchase #5	$227.48	12.497%	$255.9082	$255.91	$255.90	$255.90
Purchase #6	$31.63	5.818%	$33.4702	$33.47	$33.45	$33.50
Purchase #7	$144.97	13.155%	$164.0408	$164.04	$164.05	$164.00
7 purchase totals =	$680.96		$752.1120	$752.11	$752.10	$752.10