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	$88.31	13.644%	$100.359	$100.36	$100.35	$100.40
Purchase #2	$54.68	13.169%	$61.8808	$61.88	$61.90	$61.90
Purchase #3	$76.48	5.231%	$80.4807	$80.48	$80.50	$80.50
Purchase #4	$196.59	8.378%	$213.0603	$213.06	$213.05	$213.10
Purchase #5	$161.76	5.216%	$170.1974	$170.20	$170.20	$170.20
Purchase #6	$155.43	4.435%	$162.3233	$162.32	$162.30	$162.30
Purchase #7	$54.80	11.364%	$61.0275	$61.03	$61.05	$61.00
7 purchase totals =	$788.05		$849.3290	$849.33	$849.35	$849.40