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	$7.98	8.270%	$8.6399	$8.64	$8.65	$8.60
Purchase #2	$74.70	4.688%	$78.2019	$78.20	$78.20	$78.20
Purchase #3	$37.63	5.818%	$39.8193	$39.82	$39.80	$39.80
Purchase #4	$213.75	11.400%	$238.1175	$238.12	$238.10	$238.10
Purchase #5	$154.33	9.199%	$168.5268	$168.53	$168.55	$168.50
Purchase #6	$48.46	11.860%	$54.2074	$54.21	$54.20	$54.20
Purchase #7	$12.51	10.439%	$13.8159	$13.82	$13.80	$13.80
7 purchase totals =	$549.36		$601.3287	$601.34	$601.30	$601.20