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	$130.36	12.555%	$146.7267	$146.73	$146.75	$146.70
Purchase #2	$194.35	12.533%	$218.7079	$218.71	$218.70	$218.70
Purchase #3	$115.72	12.180%	$129.8147	$129.81	$129.80	$129.80
Purchase #4	$114.49	7.520%	$123.0996	$123.10	$123.10	$123.10
Purchase #5	$31.67	12.372%	$35.5882	$35.59	$35.60	$35.60
Purchase #6	$165.52	3.566%	$171.4224	$171.42	$171.40	$171.40
Purchase #7	$147.98	13.191%	$167.5	$167.50	$167.50	$167.50
7 purchase totals =	$900.09		$992.8595	$992.86	$992.85	$992.80