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	$98.47	12.257%	$110.5395	$110.54	$110.55	$110.50
Purchase #2	$191.43	4.397%	$199.8472	$199.85	$199.85	$199.80
Purchase #3	$189.62	13.575%	$215.3609	$215.36	$215.35	$215.40
Purchase #4	$154.79	10.585%	$171.1745	$171.17	$171.15	$171.20
Purchase #5	$29.48	5.523%	$31.1082	$31.11	$31.10	$31.10
Purchase #6	$246.60	10.496%	$272.4831	$272.48	$272.50	$272.50
Purchase #7	$99.62	11.539%	$111.1152	$111.12	$111.10	$111.10
7 purchase totals =	$1,010.01		$1,111.6286	$1,111.63	$1,111.60	$1,111.60