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	$78.55	8.380%	$85.1325	$85.13	$85.15	$85.10
Purchase #2	$89.48	11.721%	$99.968	$99.97	$99.95	$100.00
Purchase #3	$98.91	10.690%	$109.4835	$109.48	$109.50	$109.50
Purchase #4	$101.57	10.140%	$111.8692	$111.87	$111.85	$111.90
Purchase #5	$233.41	9.768%	$256.2095	$256.21	$256.20	$256.20
Purchase #6	$6.74	9.433%	$7.3758	$7.38	$7.40	$7.40
Purchase #7	$245.43	13.774%	$279.2355	$279.24	$279.25	$279.20
7 purchase totals =	$854.09		$949.2740	$949.28	$949.30	$949.30