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	$25.60	12.448%	$28.7867	$28.79	$28.80	$28.80
Purchase #2	$95.85	7.816%	$103.3416	$103.34	$103.35	$103.30
Purchase #3	$95.83	3.423%	$99.1103	$99.11	$99.10	$99.10
Purchase #4	$40.41	10.256%	$44.5544	$44.55	$44.55	$44.60
Purchase #5	$109.80	12.311%	$123.3175	$123.32	$123.30	$123.30
Purchase #6	$64.42	10.452%	$71.1532	$71.15	$71.15	$71.20
Purchase #7	$182.30	13.316%	$206.5751	$206.58	$206.60	$206.60
7 purchase totals =	$614.21		$676.8388	$676.84	$676.85	$676.90