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	$19.88	4.442%	$20.7631	$20.76	$20.75	$20.80
Purchase #2	$168.53	11.165%	$187.3464	$187.35	$187.35	$187.30
Purchase #3	$94.56	9.329%	$103.3815	$103.38	$103.40	$103.40
Purchase #4	$90.41	4.555%	$94.5282	$94.53	$94.55	$94.50
Purchase #5	$56.51	13.705%	$64.2547	$64.25	$64.25	$64.30
Purchase #6	$84.59	9.289%	$92.4476	$92.45	$92.45	$92.40
Purchase #7	$199.50	8.608%	$216.673	$216.67	$216.65	$216.70
7 purchase totals =	$713.98		$779.3945	$779.39	$779.40	$779.40