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	$176.34	7.722%	$189.957	$189.96	$189.95	$190.00
Purchase #2	$141.77	3.611%	$146.8893	$146.89	$146.90	$146.90
Purchase #3	$53.33	5.126%	$56.0637	$56.06	$56.05	$56.10
Purchase #4	$188.99	11.800%	$211.2908	$211.29	$211.30	$211.30
Purchase #5	$71.93	9.537%	$78.79	$78.79	$78.80	$78.80
Purchase #6	$100.39	9.371%	$109.7975	$109.80	$109.80	$109.80
Purchase #7	$37.61	6.409%	$40.0204	$40.02	$40.00	$40.00
7 purchase totals =	$770.36		$832.8087	$832.81	$832.80	$832.90