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	$117.95	11.256%	$131.2265	$131.23	$131.25	$131.20
Purchase #2	$101.73	10.140%	$112.0454	$112.05	$112.05	$112.00
Purchase #3	$82.71	6.847%	$88.3732	$88.37	$88.35	$88.40
Purchase #4	$40.31	6.155%	$42.7911	$42.79	$42.80	$42.80
Purchase #5	$209.30	4.515%	$218.7499	$218.75	$218.75	$218.70
Purchase #6	$12.42	11.819%	$13.8879	$13.89	$13.90	$13.90
Purchase #7	$204.99	10.646%	$226.8132	$226.81	$226.80	$226.80
7 purchase totals =	$769.41		$833.8872	$833.89	$833.90	$833.80