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	$20.83	4.515%	$21.7705	$21.77	$21.75	$21.80
Purchase #2	$72.59	7.537%	$78.0611	$78.06	$78.05	$78.10
Purchase #3	$165.69	12.167%	$185.8495	$185.85	$185.85	$185.80
Purchase #4	$89.97	12.352%	$101.0831	$101.08	$101.10	$101.10
Purchase #5	$144.63	11.409%	$161.1308	$161.13	$161.15	$161.10
Purchase #6	$89.81	3.386%	$92.851	$92.85	$92.85	$92.90
Purchase #7	$142.77	9.812%	$156.7786	$156.78	$156.80	$156.80
7 purchase totals =	$726.29		$797.5246	$797.52	$797.55	$797.60