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	$82.97	6.135%	$88.0602	$88.06	$88.05	$88.10
Purchase #2	$78.78	5.135%	$82.8254	$82.83	$82.85	$82.80
Purchase #3	$62.96	12.425%	$70.7828	$70.78	$70.80	$70.80
Purchase #4	$194.88	8.193%	$210.8465	$210.85	$210.85	$210.80
Purchase #5	$154.54	11.146%	$171.765	$171.77	$171.75	$171.80
Purchase #6	$205.29	13.766%	$233.5502	$233.55	$233.55	$233.60
Purchase #7	$64.46	12.819%	$72.7231	$72.72	$72.70	$72.70
7 purchase totals =	$843.88		$930.5532	$930.56	$930.55	$930.60