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	$67.86	7.753%	$73.1212	$73.12	$73.10	$73.10
Purchase #2	$64.65	3.114%	$66.6632	$66.66	$66.65	$66.70
Purchase #3	$64.80	4.732%	$67.8663	$67.87	$67.85	$67.90
Purchase #4	$152.77	12.285%	$171.5378	$171.54	$171.55	$171.50
Purchase #5	$97.62	6.334%	$103.8033	$103.80	$103.80	$103.80
Purchase #6	$172.73	9.353%	$188.8854	$188.89	$188.90	$188.90
Purchase #7	$84.57	12.157%	$94.8512	$94.85	$94.85	$94.90
7 purchase totals =	$705.00		$766.7284	$766.73	$766.70	$766.80