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	$128.58	9.774%	$141.1474	$141.15	$141.15	$141.10
Purchase #2	$55.98	4.440%	$58.4655	$58.47	$58.45	$58.50
Purchase #3	$28.79	10.775%	$31.8921	$31.89	$31.90	$31.90
Purchase #4	$44.40	8.850%	$48.3294	$48.33	$48.35	$48.30
Purchase #5	$123.63	4.799%	$129.563	$129.56	$129.55	$129.60
Purchase #6	$153.26	11.611%	$171.055	$171.06	$171.05	$171.10
Purchase #7	$56.95	8.165%	$61.6	$61.60	$61.60	$61.60
7 purchase totals =	$591.59		$642.0524	$642.06	$642.05	$642.10