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	$249.82	12.803%	$281.8045	$281.80	$281.80	$281.80
Purchase #2	$216.76	3.192%	$223.679	$223.68	$223.70	$223.70
Purchase #3	$78.37	5.222%	$82.4625	$82.46	$82.45	$82.50
Purchase #4	$166.80	10.575%	$184.4391	$184.44	$184.45	$184.40
Purchase #5	$81.49	6.168%	$86.5163	$86.52	$86.50	$86.50
Purchase #6	$36.86	8.568%	$40.0182	$40.02	$40.00	$40.00
Purchase #7	$6.69	10.212%	$7.3732	$7.37	$7.35	$7.40
7 purchase totals =	$836.79		$906.2928	$906.29	$906.25	$906.30