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	$183.86	6.816%	$196.3919	$196.39	$196.40	$196.40
Purchase #2	$139.82	7.772%	$150.6868	$150.69	$150.70	$150.70
Purchase #3	$210.25	5.386%	$221.5741	$221.57	$221.55	$221.60
Purchase #4	$242.32	13.481%	$274.9872	$274.99	$275.00	$275.00
Purchase #5	$172.25	5.767%	$182.1837	$182.18	$182.20	$182.20
Purchase #6	$94.66	7.328%	$101.5967	$101.60	$101.60	$101.60
Purchase #7	$84.46	11.768%	$94.3993	$94.40	$94.40	$94.40
7 purchase totals =	$1,127.62		$1,221.8197	$1,221.82	$1,221.85	$1,221.90