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	$63.92	13.854%	$72.7755	$72.78	$72.80	$72.80
Purchase #2	$88.91	4.436%	$92.854	$92.85	$92.85	$92.90
Purchase #3	$147.36	8.788%	$160.31	$160.31	$160.30	$160.30
Purchase #4	$109.62	5.208%	$115.329	$115.33	$115.35	$115.30
Purchase #5	$137.46	3.287%	$141.9783	$141.98	$142.00	$142.00
Purchase #6	$130.63	6.489%	$139.1066	$139.11	$139.10	$139.10
Purchase #7	$86.33	12.119%	$96.7923	$96.79	$96.80	$96.80
7 purchase totals =	$764.23		$819.1457	$819.15	$819.20	$819.20