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	$73.86	11.155%	$82.0991	$82.10	$82.10	$82.10
Purchase #2	$250.49	10.794%	$277.5279	$277.53	$277.55	$277.50
Purchase #3	$122.66	13.762%	$139.5405	$139.54	$139.55	$139.50
Purchase #4	$80.34	3.843%	$83.4275	$83.43	$83.45	$83.40
Purchase #5	$139.54	6.552%	$148.6827	$148.68	$148.70	$148.70
Purchase #6	$194.69	3.485%	$201.4749	$201.47	$201.45	$201.50
Purchase #7	$88.81	11.527%	$99.0471	$99.05	$99.05	$99.00
7 purchase totals =	$950.39		$1,031.7997	$1,031.80	$1,031.85	$1,031.70