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	$142.50	12.650%	$160.5263	$160.53	$160.55	$160.50
Purchase #2	$19.47	12.357%	$21.8759	$21.88	$21.90	$21.90
Purchase #3	$116.33	4.473%	$121.5334	$121.53	$121.55	$121.50
Purchase #4	$221.72	13.144%	$250.8629	$250.86	$250.85	$250.90
Purchase #5	$25.97	10.611%	$28.7257	$28.73	$28.75	$28.70
Purchase #6	$90.66	7.341%	$97.3154	$97.32	$97.30	$97.30
Purchase #7	$79.58	12.432%	$89.4734	$89.47	$89.45	$89.50
7 purchase totals =	$696.23		$770.3130	$770.32	$770.35	$770.30