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	$50.95	13.570%	$57.8639	$57.86	$57.85	$57.90
Purchase #2	$123.79	7.141%	$132.6298	$132.63	$132.65	$132.60
Purchase #3	$209.86	10.668%	$232.2479	$232.25	$232.25	$232.20
Purchase #4	$80.44	11.449%	$89.6496	$89.65	$89.65	$89.60
Purchase #5	$207.77	6.535%	$221.3478	$221.35	$221.35	$221.30
Purchase #6	$24.30	3.272%	$25.0951	$25.10	$25.10	$25.10
Purchase #7	$77.71	10.323%	$85.732	$85.73	$85.75	$85.70
7 purchase totals =	$774.82		$844.5661	$844.57	$844.60	$844.40