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	$96.94	3.507%	$100.3397	$100.34	$100.35	$100.30
Purchase #2	$134.80	12.858%	$152.1326	$152.13	$152.15	$152.10
Purchase #3	$40.73	3.661%	$42.2211	$42.22	$42.20	$42.20
Purchase #4	$116.94	5.408%	$123.2641	$123.26	$123.25	$123.30
Purchase #5	$155.89	9.719%	$171.0409	$171.04	$171.05	$171.00
Purchase #6	$110.49	12.842%	$124.6791	$124.68	$124.70	$124.70
Purchase #7	$156.41	6.340%	$166.3264	$166.33	$166.35	$166.30
7 purchase totals =	$812.20		$880.0039	$880.00	$880.05	$879.90