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	$170.34	10.818%	$188.7674	$188.77	$188.75	$188.80
Purchase #2	$150.89	13.330%	$171.0036	$171.00	$171.00	$171.00
Purchase #3	$90.73	4.553%	$94.8609	$94.86	$94.85	$94.90
Purchase #4	$53.87	13.243%	$61.004	$61.00	$61.00	$61.00
Purchase #5	$75.43	6.646%	$80.4431	$80.44	$80.45	$80.40
Purchase #6	$79.57	3.847%	$82.6311	$82.63	$82.65	$82.60
Purchase #7	$235.75	13.418%	$267.3829	$267.38	$267.40	$267.40
7 purchase totals =	$856.58		$946.0930	$946.08	$946.10	$946.10