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	$203.68	4.710%	$213.2733	$213.27	$213.25	$213.30
Purchase #2	$66.69	8.706%	$72.496	$72.50	$72.50	$72.50
Purchase #3	$41.54	11.603%	$46.3599	$46.36	$46.35	$46.40
Purchase #4	$98.61	12.109%	$110.5507	$110.55	$110.55	$110.60
Purchase #5	$53.51	11.435%	$59.6289	$59.63	$59.65	$59.60
Purchase #6	$190.96	10.619%	$211.238	$211.24	$211.25	$211.20
Purchase #7	$117.33	9.233%	$128.1631	$128.16	$128.15	$128.20
7 purchase totals =	$772.32		$841.7099	$841.71	$841.70	$841.80