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	$189.80	3.606%	$196.6442	$196.64	$196.65	$196.60
Purchase #2	$219.28	12.865%	$247.4904	$247.49	$247.50	$247.50
Purchase #3	$10.88	10.531%	$12.0258	$12.03	$12.05	$12.00
Purchase #4	$191.40	12.505%	$215.3346	$215.33	$215.35	$215.30
Purchase #5	$51.66	10.617%	$57.1447	$57.14	$57.15	$57.10
Purchase #6	$89.54	7.610%	$96.354	$96.35	$96.35	$96.40
Purchase #7	$211.44	10.202%	$233.0111	$233.01	$233.00	$233.00
7 purchase totals =	$964.00		$1,058.0048	$1,057.99	$1,058.05	$1,057.90