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	$86.88	4.169%	$90.502	$90.50	$90.50	$90.50
Purchase #2	$146.98	13.376%	$166.64	$166.64	$166.65	$166.60
Purchase #3	$36.89	10.765%	$40.8612	$40.86	$40.85	$40.90
Purchase #4	$240.46	10.343%	$265.3308	$265.33	$265.35	$265.30
Purchase #5	$72.53	11.593%	$80.9384	$80.94	$80.95	$80.90
Purchase #6	$219.38	11.465%	$244.5319	$244.53	$244.55	$244.50
Purchase #7	$207.27	5.736%	$219.159	$219.16	$219.15	$219.20
7 purchase totals =	$1,010.39		$1,107.9633	$1,107.96	$1,108.00	$1,107.90