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	$39.45	6.713%	$42.0983	$42.10	$42.10	$42.10
Purchase #2	$127.53	9.399%	$139.5165	$139.52	$139.50	$139.50
Purchase #3	$97.36	12.399%	$109.4317	$109.43	$109.45	$109.40
Purchase #4	$240.26	3.293%	$248.1718	$248.17	$248.15	$248.20
Purchase #5	$191.77	11.353%	$213.5416	$213.54	$213.55	$213.50
Purchase #6	$119.36	7.419%	$128.2153	$128.22	$128.20	$128.20
Purchase #7	$199.67	12.216%	$224.0617	$224.06	$224.05	$224.10
7 purchase totals =	$1,015.40		$1,105.0369	$1,105.04	$1,105.00	$1,105.00