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	$27.33	5.835%	$28.9247	$28.92	$28.90	$28.90
Purchase #2	$206.33	7.554%	$221.9162	$221.92	$221.90	$221.90
Purchase #3	$75.45	8.709%	$82.0209	$82.02	$82.00	$82.00
Purchase #4	$65.53	10.518%	$72.4224	$72.42	$72.40	$72.40
Purchase #5	$246.45	5.834%	$260.8279	$260.83	$260.85	$260.80
Purchase #6	$155.48	8.581%	$168.8217	$168.82	$168.80	$168.80
Purchase #7	$50.56	7.759%	$54.483	$54.48	$54.50	$54.50
7 purchase totals =	$827.13		$889.4168	$889.41	$889.35	$889.30