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	$156.81	13.510%	$177.995	$178.00	$178.00	$178.00
Purchase #2	$94.49	9.155%	$103.1406	$103.14	$103.15	$103.10
Purchase #3	$201.55	6.655%	$214.9632	$214.96	$214.95	$215.00
Purchase #4	$98.70	6.539%	$105.154	$105.15	$105.15	$105.20
Purchase #5	$60.72	10.785%	$67.2687	$67.27	$67.25	$67.30
Purchase #6	$64.36	12.623%	$72.4842	$72.48	$72.50	$72.50
Purchase #7	$148.86	10.706%	$164.797	$164.80	$164.80	$164.80
7 purchase totals =	$825.49		$905.8027	$905.80	$905.80	$905.90