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	$86.76	13.592%	$98.5524	$98.55	$98.55	$98.60
Purchase #2	$115.51	13.675%	$131.306	$131.31	$131.30	$131.30
Purchase #3	$120.35	9.300%	$131.5426	$131.54	$131.55	$131.50
Purchase #4	$42.41	6.212%	$45.0445	$45.04	$45.05	$45.00
Purchase #5	$6.79	12.458%	$7.6359	$7.64	$7.65	$7.60
Purchase #6	$69.69	11.214%	$77.505	$77.51	$77.50	$77.50
Purchase #7	$130.75	5.357%	$137.7543	$137.75	$137.75	$137.80
7 purchase totals =	$572.26		$629.3407	$629.34	$629.35	$629.30