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	$21.58	9.242%	$23.5744	$23.57	$23.55	$23.60
Purchase #2	$41.46	9.467%	$45.385	$45.39	$45.40	$45.40
Purchase #3	$239.36	10.368%	$264.1768	$264.18	$264.20	$264.20
Purchase #4	$132.84	6.828%	$141.9103	$141.91	$141.90	$141.90
Purchase #5	$156.67	10.729%	$173.4791	$173.48	$173.50	$173.50
Purchase #6	$98.47	11.473%	$109.7675	$109.77	$109.75	$109.80
Purchase #7	$89.55	12.535%	$100.7751	$100.78	$100.80	$100.80
7 purchase totals =	$779.93		$859.0682	$859.08	$859.10	$859.20