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	$55.38	5.433%	$58.3888	$58.39	$58.40	$58.40
Purchase #2	$146.59	12.646%	$165.1278	$165.13	$165.15	$165.10
Purchase #3	$133.73	4.470%	$139.7077	$139.71	$139.70	$139.70
Purchase #4	$215.67	12.685%	$243.0277	$243.03	$243.05	$243.00
Purchase #5	$232.78	5.370%	$245.2803	$245.28	$245.30	$245.30
Purchase #6	$153.48	11.672%	$171.3942	$171.39	$171.40	$171.40
Purchase #7	$77.94	6.299%	$82.8494	$82.85	$82.85	$82.80
7 purchase totals =	$1,015.57		$1,105.7759	$1,105.78	$1,105.85	$1,105.70