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	$191.38	3.522%	$198.1204	$198.12	$198.10	$198.10
Purchase #2	$56.86	8.740%	$61.8296	$61.83	$61.85	$61.80
Purchase #3	$14.33	7.368%	$15.3858	$15.39	$15.40	$15.40
Purchase #4	$116.37	4.758%	$121.9069	$121.91	$121.90	$121.90
Purchase #5	$134.98	3.678%	$139.9446	$139.94	$139.95	$139.90
Purchase #6	$223.33	8.459%	$242.2215	$242.22	$242.20	$242.20
Purchase #7	$94.34	6.421%	$100.3976	$100.40	$100.40	$100.40
7 purchase totals =	$831.59		$879.8064	$879.81	$879.80	$879.70