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	$244.72	10.736%	$270.9931	$270.99	$271.00	$271.00
Purchase #2	$175.65	4.858%	$184.1831	$184.18	$184.20	$184.20
Purchase #3	$45.96	10.661%	$50.8598	$50.86	$50.85	$50.90
Purchase #4	$179.74	9.539%	$196.8854	$196.89	$196.90	$196.90
Purchase #5	$6.28	3.148%	$6.4777	$6.48	$6.50	$6.50
Purchase #6	$200.50	9.650%	$219.8483	$219.85	$219.85	$219.80
Purchase #7	$133.38	7.691%	$143.6383	$143.64	$143.65	$143.60
7 purchase totals =	$986.23		$1,072.8857	$1,072.89	$1,072.95	$1,072.90