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	$26.59	8.305%	$28.7983	$28.80	$28.80	$28.80
Purchase #2	$17.57	4.654%	$18.3877	$18.39	$18.40	$18.40
Purchase #3	$133.40	5.377%	$140.5729	$140.57	$140.55	$140.60
Purchase #4	$69.47	13.456%	$78.8179	$78.82	$78.80	$78.80
Purchase #5	$88.83	5.402%	$93.6286	$93.63	$93.65	$93.60
Purchase #6	$83.33	9.834%	$91.5247	$91.52	$91.50	$91.50
Purchase #7	$178.26	10.474%	$196.931	$196.93	$196.95	$196.90
7 purchase totals =	$597.45		$648.6611	$648.66	$648.65	$648.60