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	$112.78	13.704%	$128.2354	$128.24	$128.25	$128.20
Purchase #2	$36.68	5.281%	$38.6171	$38.62	$38.60	$38.60
Purchase #3	$225.72	4.244%	$235.2996	$235.30	$235.30	$235.30
Purchase #4	$60.29	9.650%	$66.108	$66.11	$66.10	$66.10
Purchase #5	$175.43	11.871%	$196.2553	$196.26	$196.25	$196.30
Purchase #6	$31.98	11.140%	$35.5426	$35.54	$35.55	$35.50
Purchase #7	$82.60	10.309%	$91.1152	$91.12	$91.10	$91.10
7 purchase totals =	$725.48		$791.1732	$791.19	$791.15	$791.10