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	$206.99	13.480%	$234.8923	$234.89	$234.90	$234.90
Purchase #2	$85.32	4.803%	$89.4179	$89.42	$89.40	$89.40
Purchase #3	$31.82	10.779%	$35.2499	$35.25	$35.25	$35.20
Purchase #4	$187.60	12.795%	$211.6034	$211.60	$211.60	$211.60
Purchase #5	$13.31	11.652%	$14.8609	$14.86	$14.85	$14.90
Purchase #6	$136.36	13.331%	$154.5382	$154.54	$154.55	$154.50
Purchase #7	$209.55	4.234%	$218.4223	$218.42	$218.40	$218.40
7 purchase totals =	$870.95		$958.9849	$958.98	$958.95	$958.90