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	$38.51	5.510%	$40.6319	$40.63	$40.65	$40.60
Purchase #2	$194.73	9.605%	$213.4338	$213.43	$213.45	$213.40
Purchase #3	$170.33	7.380%	$182.9004	$182.90	$182.90	$182.90
Purchase #4	$117.50	11.838%	$131.4097	$131.41	$131.40	$131.40
Purchase #5	$144.78	9.361%	$158.3329	$158.33	$158.35	$158.30
Purchase #6	$197.27	13.468%	$223.8383	$223.84	$223.85	$223.80
Purchase #7	$165.88	13.782%	$188.7416	$188.74	$188.75	$188.70
7 purchase totals =	$1,029.00		$1,139.2886	$1,139.28	$1,139.35	$1,139.10