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	$138.35	12.424%	$155.5386	$155.54	$155.55	$155.50
Purchase #2	$241.76	5.564%	$255.2115	$255.21	$255.20	$255.20
Purchase #3	$26.25	5.366%	$27.6586	$27.66	$27.65	$27.70
Purchase #4	$98.39	11.130%	$109.3408	$109.34	$109.35	$109.30
Purchase #5	$132.38	7.606%	$142.4488	$142.45	$142.45	$142.40
Purchase #6	$60.32	13.813%	$68.652	$68.65	$68.65	$68.70
Purchase #7	$245.34	7.761%	$264.3808	$264.38	$264.40	$264.40
7 purchase totals =	$942.79		$1,023.2311	$1,023.23	$1,023.25	$1,023.20