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	$71.54	9.673%	$78.4601	$78.46	$78.45	$78.50
Purchase #2	$152.33	12.690%	$171.6607	$171.66	$171.65	$171.70
Purchase #3	$103.50	12.129%	$116.0535	$116.05	$116.05	$116.10
Purchase #4	$6.57	12.245%	$7.3745	$7.37	$7.35	$7.40
Purchase #5	$192.63	3.644%	$199.6494	$199.65	$199.65	$199.60
Purchase #6	$176.97	9.800%	$194.3131	$194.31	$194.30	$194.30
Purchase #7	$199.98	9.399%	$218.7761	$218.78	$218.80	$218.80
7 purchase totals =	$903.52		$986.2874	$986.28	$986.25	$986.40