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	$138.89	5.720%	$146.8345	$146.83	$146.85	$146.80
Purchase #2	$144.26	8.681%	$156.7832	$156.78	$156.80	$156.80
Purchase #3	$57.69	12.691%	$65.0114	$65.01	$65.00	$65.00
Purchase #4	$166.50	5.547%	$175.7358	$175.74	$175.75	$175.70
Purchase #5	$81.76	8.218%	$88.479	$88.48	$88.50	$88.50
Purchase #6	$81.51	6.566%	$86.8619	$86.86	$86.85	$86.90
Purchase #7	$125.98	9.455%	$137.8914	$137.89	$137.90	$137.90
7 purchase totals =	$796.59		$857.5972	$857.59	$857.65	$857.60