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	$89.51	10.736%	$99.1198	$99.12	$99.10	$99.10
Purchase #2	$250.61	11.515%	$279.4677	$279.47	$279.45	$279.50
Purchase #3	$200.46	4.399%	$209.2782	$209.28	$209.30	$209.30
Purchase #4	$72.96	9.793%	$80.105	$80.11	$80.10	$80.10
Purchase #5	$64.37	13.109%	$72.8083	$72.81	$72.80	$72.80
Purchase #6	$114.58	4.558%	$119.8026	$119.80	$119.80	$119.80
Purchase #7	$211.36	13.118%	$239.0862	$239.09	$239.10	$239.10
7 purchase totals =	$1,003.85		$1,099.6678	$1,099.68	$1,099.65	$1,099.70