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	$117.37	5.494%	$123.8183	$123.82	$123.80	$123.80
Purchase #2	$171.96	11.377%	$191.5239	$191.52	$191.50	$191.50
Purchase #3	$12.63	7.558%	$13.5846	$13.58	$13.60	$13.60
Purchase #4	$157.48	9.173%	$171.9256	$171.93	$171.95	$171.90
Purchase #5	$6.79	10.355%	$7.4931	$7.49	$7.50	$7.50
Purchase #6	$221.46	6.512%	$235.8815	$235.88	$235.90	$235.90
Purchase #7	$77.77	9.526%	$85.1784	$85.18	$85.20	$85.20
7 purchase totals =	$765.46		$829.4054	$829.40	$829.45	$829.40