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	$82.48	9.329%	$90.1746	$90.17	$90.15	$90.20
Purchase #2	$142.33	11.610%	$158.8545	$158.85	$158.85	$158.90
Purchase #3	$96.83	6.734%	$103.3505	$103.35	$103.35	$103.40
Purchase #4	$158.49	7.237%	$169.9599	$169.96	$169.95	$170.00
Purchase #5	$167.98	3.804%	$174.37	$174.37	$174.35	$174.40
Purchase #6	$64.40	9.267%	$70.3679	$70.37	$70.35	$70.40
Purchase #7	$25.25	8.822%	$27.4776	$27.48	$27.50	$27.50
7 purchase totals =	$737.76		$794.5550	$794.55	$794.50	$794.80