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	$35.78	12.420%	$40.2239	$40.22	$40.20	$40.20
Purchase #2	$85.55	5.332%	$90.1115	$90.11	$90.10	$90.10
Purchase #3	$22.41	10.787%	$24.8274	$24.83	$24.85	$24.80
Purchase #4	$66.40	9.528%	$72.7266	$72.73	$72.75	$72.70
Purchase #5	$144.48	9.556%	$158.2865	$158.29	$158.30	$158.30
Purchase #6	$167.43	11.666%	$186.9624	$186.96	$186.95	$187.00
Purchase #7	$75.32	11.217%	$83.7686	$83.77	$83.75	$83.80
7 purchase totals =	$597.37		$656.9069	$656.91	$656.90	$656.90