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	$70.77	8.157%	$76.5427	$76.54	$76.55	$76.50
Purchase #2	$174.49	9.545%	$191.1451	$191.15	$191.15	$191.10
Purchase #3	$128.52	7.649%	$138.3505	$138.35	$138.35	$138.40
Purchase #4	$135.31	3.668%	$140.2732	$140.27	$140.25	$140.30
Purchase #5	$29.59	12.654%	$33.3343	$33.33	$33.35	$33.30
Purchase #6	$250.32	9.540%	$274.2005	$274.20	$274.20	$274.20
Purchase #7	$18.31	12.131%	$20.5312	$20.53	$20.55	$20.50
7 purchase totals =	$807.31		$874.3775	$874.37	$874.40	$874.30