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	$8.31	5.598%	$8.7752	$8.78	$8.80	$8.80
Purchase #2	$220.69	11.199%	$245.4051	$245.41	$245.40	$245.40
Purchase #3	$219.28	13.518%	$248.9223	$248.92	$248.90	$248.90
Purchase #4	$186.47	7.552%	$200.5522	$200.55	$200.55	$200.60
Purchase #5	$97.72	9.496%	$106.9995	$107.00	$107.00	$107.00
Purchase #6	$94.82	4.799%	$99.3704	$99.37	$99.35	$99.40
Purchase #7	$143.61	13.401%	$162.8552	$162.86	$162.85	$162.90
7 purchase totals =	$970.90		$1,072.8799	$1,072.89	$1,072.85	$1,073.00