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	$227.26	9.647%	$249.1838	$249.18	$249.20	$249.20
Purchase #2	$108.31	3.207%	$111.7835	$111.78	$111.80	$111.80
Purchase #3	$173.91	12.850%	$196.2574	$196.26	$196.25	$196.30
Purchase #4	$243.29	13.765%	$276.7789	$276.78	$276.80	$276.80
Purchase #5	$207.34	5.590%	$218.9303	$218.93	$218.95	$218.90
Purchase #6	$156.50	7.644%	$168.4629	$168.46	$168.45	$168.50
Purchase #7	$206.35	3.550%	$213.6754	$213.68	$213.70	$213.70
7 purchase totals =	$1,322.96		$1,435.0722	$1,435.07	$1,435.15	$1,435.20