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	$96.66	10.168%	$106.4884	$106.49	$106.50	$106.50
Purchase #2	$243.27	3.134%	$250.8941	$250.89	$250.90	$250.90
Purchase #3	$130.59	13.649%	$148.4142	$148.41	$148.40	$148.40
Purchase #4	$82.57	6.689%	$88.0931	$88.09	$88.10	$88.10
Purchase #5	$59.84	4.865%	$62.7512	$62.75	$62.75	$62.80
Purchase #6	$184.28	12.265%	$206.8819	$206.88	$206.90	$206.90
Purchase #7	$118.54	4.137%	$123.444	$123.44	$123.45	$123.40
7 purchase totals =	$915.75		$986.9669	$986.95	$987.00	$987.00