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	$136.48	7.200%	$146.3066	$146.31	$146.30	$146.30
Purchase #2	$140.80	6.515%	$149.9731	$149.97	$149.95	$150.00
Purchase #3	$88.96	12.464%	$100.048	$100.05	$100.05	$100.00
Purchase #4	$114.72	7.308%	$123.1037	$123.10	$123.10	$123.10
Purchase #5	$242.79	4.212%	$253.0163	$253.02	$253.00	$253.00
Purchase #6	$67.34	6.706%	$71.8558	$71.86	$71.85	$71.90
Purchase #7	$34.47	5.731%	$36.4455	$36.45	$36.45	$36.40
7 purchase totals =	$825.56		$880.7490	$880.76	$880.70	$880.70