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	$95.49	5.131%	$100.3896	$100.39	$100.40	$100.40
Purchase #2	$195.69	9.112%	$213.5213	$213.52	$213.50	$213.50
Purchase #3	$62.54	7.320%	$67.1179	$67.12	$67.10	$67.10
Purchase #4	$182.34	12.596%	$205.3075	$205.31	$205.30	$205.30
Purchase #5	$201.90	9.129%	$220.3315	$220.33	$220.35	$220.30
Purchase #6	$31.30	10.637%	$34.6294	$34.63	$34.65	$34.60
Purchase #7	$85.40	4.322%	$89.091	$89.09	$89.10	$89.10
7 purchase totals =	$854.66		$930.3882	$930.39	$930.40	$930.30