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	$39.56	13.854%	$45.0406	$45.04	$45.05	$45.00
Purchase #2	$214.72	12.230%	$240.9803	$240.98	$241.00	$241.00
Purchase #3	$115.37	8.459%	$125.1291	$125.13	$125.15	$125.10
Purchase #4	$43.48	3.148%	$44.8488	$44.85	$44.85	$44.80
Purchase #5	$80.27	11.467%	$89.4746	$89.47	$89.45	$89.50
Purchase #6	$26.90	6.279%	$28.5891	$28.59	$28.60	$28.60
Purchase #7	$60.36	13.479%	$68.4959	$68.50	$68.50	$68.50
7 purchase totals =	$580.66		$642.5584	$642.56	$642.60	$642.50