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	$200.53	6.200%	$212.9629	$212.96	$212.95	$213.00
Purchase #2	$55.34	12.800%	$62.4235	$62.42	$62.40	$62.40
Purchase #3	$89.32	7.491%	$96.011	$96.01	$96.00	$96.00
Purchase #4	$231.86	9.315%	$253.4578	$253.46	$253.45	$253.50
Purchase #5	$78.62	13.372%	$89.1331	$89.13	$89.15	$89.10
Purchase #6	$126.37	10.568%	$139.7248	$139.72	$139.70	$139.70
Purchase #7	$150.26	3.520%	$155.5492	$155.55	$155.55	$155.50
7 purchase totals =	$932.30		$1,009.2623	$1,009.25	$1,009.20	$1,009.20