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	$149.73	7.125%	$160.3983	$160.40	$160.40	$160.40
Purchase #2	$248.37	12.227%	$278.7382	$278.74	$278.75	$278.70
Purchase #3	$63.63	11.858%	$71.1752	$71.18	$71.20	$71.20
Purchase #4	$25.38	12.740%	$28.6134	$28.61	$28.60	$28.60
Purchase #5	$186.80	5.228%	$196.5659	$196.57	$196.55	$196.60
Purchase #6	$237.26	3.495%	$245.5522	$245.55	$245.55	$245.60
Purchase #7	$107.27	11.469%	$119.5728	$119.57	$119.55	$119.60
7 purchase totals =	$1,018.44		$1,100.6160	$1,100.62	$1,100.60	$1,100.70