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	$39.29	4.711%	$41.141	$41.14	$41.15	$41.10
Purchase #2	$218.80	9.194%	$238.9165	$238.92	$238.90	$238.90
Purchase #3	$88.90	11.675%	$99.2791	$99.28	$99.30	$99.30
Purchase #4	$59.80	5.872%	$63.3115	$63.31	$63.30	$63.30
Purchase #5	$32.77	8.263%	$35.4778	$35.48	$35.50	$35.50
Purchase #6	$22.76	9.192%	$24.8521	$24.85	$24.85	$24.90
Purchase #7	$150.32	7.786%	$162.0239	$162.02	$162.00	$162.00
7 purchase totals =	$612.64		$665.0019	$665.00	$665.00	$665.00