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	$170.72	9.483%	$186.9094	$186.91	$186.90	$186.90
Purchase #2	$47.38	6.165%	$50.301	$50.30	$50.30	$50.30
Purchase #3	$205.44	7.562%	$220.9754	$220.98	$221.00	$221.00
Purchase #4	$131.28	10.703%	$145.3309	$145.33	$145.35	$145.30
Purchase #5	$173.97	13.184%	$196.9062	$196.91	$196.90	$196.90
Purchase #6	$222.50	12.574%	$250.4772	$250.48	$250.50	$250.50
Purchase #7	$170.74	5.768%	$180.5883	$180.59	$180.60	$180.60
7 purchase totals =	$1,122.03		$1,231.4884	$1,231.50	$1,231.55	$1,231.50