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	$160.27	4.831%	$168.0126	$168.01	$168.00	$168.00
Purchase #2	$93.84	9.781%	$103.0185	$103.02	$103.00	$103.00
Purchase #3	$197.53	7.534%	$212.4119	$212.41	$212.40	$212.40
Purchase #4	$160.45	7.473%	$172.4404	$172.44	$172.45	$172.40
Purchase #5	$10.73	7.778%	$11.5646	$11.56	$11.55	$11.60
Purchase #6	$116.91	12.322%	$131.3157	$131.32	$131.30	$131.30
Purchase #7	$110.86	6.252%	$117.791	$117.79	$117.80	$117.80
7 purchase totals =	$850.59		$916.5547	$916.55	$916.50	$916.50