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	$229.47	3.213%	$236.8429	$236.84	$236.85	$236.80
Purchase #2	$203.55	9.181%	$222.2379	$222.24	$222.25	$222.20
Purchase #3	$243.76	7.713%	$262.5612	$262.56	$262.55	$262.60
Purchase #4	$20.89	9.709%	$22.9182	$22.92	$22.90	$22.90
Purchase #5	$43.85	7.696%	$47.2247	$47.22	$47.20	$47.20
Purchase #6	$83.73	7.321%	$89.8599	$89.86	$89.85	$89.90
Purchase #7	$30.29	8.416%	$32.8392	$32.84	$32.85	$32.80
7 purchase totals =	$855.54		$914.4840	$914.48	$914.45	$914.40