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	$83.64	7.765%	$90.1346	$90.13	$90.15	$90.10
Purchase #2	$7.41	6.677%	$7.9048	$7.90	$7.90	$7.90
Purchase #3	$238.51	12.241%	$267.706	$267.71	$267.70	$267.70
Purchase #4	$26.31	11.336%	$29.2925	$29.29	$29.30	$29.30
Purchase #5	$73.81	6.115%	$78.3235	$78.32	$78.30	$78.30
Purchase #6	$43.25	6.841%	$46.2087	$46.21	$46.20	$46.20
Purchase #7	$99.34	3.448%	$102.7652	$102.77	$102.75	$102.80
7 purchase totals =	$572.27		$622.3353	$622.33	$622.30	$622.30