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	$99.68	3.700%	$103.3682	$103.37	$103.35	$103.40
Purchase #2	$22.83	6.602%	$24.3372	$24.34	$24.35	$24.30
Purchase #3	$201.47	7.142%	$215.859	$215.86	$215.85	$215.90
Purchase #4	$95.28	9.676%	$104.4993	$104.50	$104.50	$104.50
Purchase #5	$119.59	11.655%	$133.5282	$133.53	$133.55	$133.50
Purchase #6	$115.47	3.362%	$119.3521	$119.35	$119.35	$119.40
Purchase #7	$160.94	6.798%	$171.8807	$171.88	$171.90	$171.90
7 purchase totals =	$815.26		$872.8247	$872.83	$872.85	$872.90